kitty: add servo overlay for kitty

Add servo overlay for kitty with the following features:
  - 'rec_mode' to control recovery button;
  - 'power_state' to control power button (not issuing EC command, in
    case EC is removed);
  - use USB_KM232 cable for FAFT tests.

BUG=chrome-os-partner:33531,chrome-os-partner:33063
TEST="sudo servod --board=nyan_kitty --usbkm32=$USBKM232_UART_DEVICE"
     pass firmware_FAFTSetup and firmware_DevMode tests

Change-Id: Icd7685449e7e12757ad8f98081d69520dcd61181
Signed-off-by: Yen Lin <yelin@nvidia.com>
Reviewed-on: https://chromium-review.googlesource.com/229521
Reviewed-by: Shawn Nematbakhsh <shawnn@chromium.org>
4 files changed