riscv: Add Kendryte KD233 board device tree

Add the device tree canaan_kd233.dts for the Canaan Kendryte KD233
development board.  This device tree enables LEDs, some gpios and
spi/mmc SD card device. The WS2812B RGB LED and the 10 positions rotary
dip switch present on the board are left undefined.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
[Palmer: Remove undocumented microphone entry, along with the use.]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>