cranky: Add usbkm232 support for cranky

Add the usbkm232 support for cranky

BUG=none
TEST=manual
1.export USBKM232_UART_DEVICE = /dev/ttyUSB0
2.sudo servod --board=cranky --usbkm232=$USBKM232_UART_DEVICE
3.there is no error messages

Change-Id: Icd9316fc2ed56f821f2bf0a2f73cecbc92b2156e
Reviewed-on: https://chromium-review.googlesource.com/229549
Reviewed-by: Shawn Nematbakhsh <shawnn@chromium.org>
Commit-Queue: 元亨 盧 <eddylu@ami.com.tw>
Tested-by: 元亨 盧 <eddylu@ami.com.tw>
1 file changed