Inital port of xd84 (#5164)

* Inital port of xd84

* Inital port of xd84 - review comments

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+# XD84
+
+Development docs covering the following:
+- Kimera core
+- RGB
+- Backlight
+
+## Kimera core
+![Kimera core](https://gd2.alicdn.com/imgextra/i4/159916802/TB2qsIgdrJkpuFjy1zcXXa5FFXa_!!159916802.jpg)
+
+What little available info that was available for the qmk port
+- atmega32u4 16Mhz
+  - board seems to have a 6Mhz crystal 
+- 2x PCA9555 I2C IO expander
+
+Links:
+- [Schematic, BOM, Gerbers](/kairyu/kimera/blob/master/kimera_core)
+- [Original firmware](https://github.com/kairyu/tmk_keyboard_custom/tree/master/keyboard/kimera)
+
+```c
+/*
+Kimera_core_v1.0 Components
+
+             U1 (atmega32u4)
+           ,----------------.
+      TX --| TX0(PD3)   RAW |--
+      RX --| RX1(PD2)   GND |--
+         --| GND      RESET |-- RST
+         --| GND        VCC |--
+     SDA --| 2(PD1) (PF4)A3 |--
+     SCL --| 3(PD0) (PF5)A2 |--
+   (INT) --| 4(PD4) (PF6)A1 |--
+         --| 5(PC6) (PF7)A0 |--
+         --| 6(PD7) (PB1)15 |-- SCK
+    LED2 --| 7(PE6) (PB3)14 |-- MISO
+    LED1 --| 8(PB4) (PB2)16 |-- MOSI
+    LED3 --| 9(PB5) (PB6)10 |-- LED4
+          `----------------'
+
+         IC1 (PCA9555)                  IC2 (PCA9555)
+         ,----------.                   ,----------.
+   SDA --| SDA  P00 |-- P1        SDA --| SDA  P00 |-- P17
+   SCL --| SCL  P01 |-- P2        SCL --| SCL  P01 |-- P18
+   INT --| INT  P02 |-- P3        INT --| INT  P02 |-- P19
+         |      P03 |-- P4              |      P03 |-- P20
+   GND --| A0   P04 |-- P5        VCC --| A0   P04 |-- P21
+   SJ1 --| A1   P05 |-- P6        SJ1 --| A1   P05 |-- P22
+   SJ2 --| A2   P06 |-- P7        SJ2 --| A2   P06 |-- P23
+         |      P07 |-- P8              |      P07 |-- P24
+         |          |                   |          |
+         |      P10 |-- P9              |      P10 |-- P25
+         |      P11 |-- P10             |      P11 |-- P26
+         |      P12 |-- P11             |      P12 |-- P27
+         |      P13 |-- P12             |      P13 |-- P28
+         |      P14 |-- P13             |      P14 |-- P29
+         |      P15 |-- P14             |      P15 |-- P30
+         |      P16 |-- P15             |      P16 |-- P31
+         |      P17 |-- P16             |      P17 |-- P32
+         `----------'                   `----------'
+*/
+
+```
+
+### Bootloader
+Default bootloader is `atmel-dfu`.
+Reboot to bootloader via magnetic switch next to icsp header.
+Flash using regular dfu methods.
+
+### XD84 pin mappings
+Taken from [kimera-config.json](https://github.com/kairyu/tkg/blob/master/keyboard/config/kimera-config.json)
+
+	"row_mapping": [ 1, 2, 3, 4, 5, 6 ],
+	"col_mapping": [ 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 ],
+
+# RGB
+- PIN C7
+- Number of RGB LED 7
+
+# Backlight
+    TODO - not working
+
+## Assumptions
+### Pin/Port mappings
+- All cols are on the same IC
+- All rows are on the same IC and port
+- Pins mapped sequentially
+- Each port only does row or column not a mixture of both
+  - No need to have complex port config
+  - 
+
+| ROW index | Kimera Pin | PCA9555           |
+| ----------|------------|-------------------|
+| 0         | 1          | IC1 Port 0  pin 0 |
+| 1         | 2          | IC1 Port 0  pin 1 |
+| 2         | 3          | IC1 Port 0  pin 2 |
+| 3         | 4          | IC1 Port 0  pin 3 |
+| 4         | 5          | IC1 Port 0  pin 4 |
+| 5         | 6          | IC1 Port 0  pin 5 |
+
+- Safe enough to assume `row_index == pin`
+
+
+| COL index | Kimera Pin | PCA9555           |
+| ----------|------------|-------------------|
+| 0         | 17         | IC2 Port 0  pin 0 |
+| 1         | 18         | IC2 Port 0  pin 1 |
+| 2         | 19         | IC2 Port 0  pin 2 |
+| 3         | 20         | IC2 Port 0  pin 3 |
+| 4         | 21         | IC2 Port 0  pin 4 |
+| 5         | 22         | IC2 Port 0  pin 5 |
+| 6         | 23         | IC2 Port 0  pin 6 |
+| 7         | 24         | IC2 Port 0  pin 7 |
+| 8         | 25         | IC2 Port 1  pin 0 |
+| 9         | 26         | IC2 Port 1  pin 1 |
+| 10        | 27         | IC2 Port 1  pin 2 |
+| 11        | 28         | IC2 Port 1  pin 3 |
+| 12        | 29         | IC2 Port 1  pin 4 |
+| 13        | 30         | IC2 Port 1  pin 5 |
+| 14        | 31         | IC2 Port 1  pin 6 |
+
+- Safe enough to assume here col_index does not need to be converted to pin
+- Reading both ports one after the other gives us the same sequential behavior
+  - maps to the usual practice of reading matrix columns
+  - while this technically gives 16 column reads, the 16th column can never be set so is safely ignored
+
+## Notes
+[pca9555 datasheet](https://www.ti.com/lit/ds/symlink/pca9555.pdf)
+
+- Other Kimera based boards with non sequential pin mappings, pins mapped across ICs, or mixed row/col configs will need more complicated `pin -> i2c_addr,port,pin` logic as well as rather more complex pin functions.
+
+## Return to stock firmware
+Not tested but original firmware seems to be available in the [kairyu/tkg-firmware](https://github.com/kairyu/tkg-firmware/blob/master/kimera-core.hex) repo.