servo_micro: add usbpd aliases

This can be used for chocodile flashing, or other flash_ec
functionality that uses the pd uart.

BUG=None
TEST=flash_ec on chocodile, all dut controls worked.

Change-Id: I751aec722223cbf62d61a69b8328ab36cd6998ad
Reviewed-on: https://chromium-review.googlesource.com/1142824
Commit-Ready: Nick Sanders <nsanders@chromium.org>
Tested-by: Nick Sanders <nsanders@chromium.org>
Reviewed-by: David Schneider <dnschneid@chromium.org>
Reviewed-by: Mary Ruthven <mruthven@chromium.org>
1 file changed