faft: Add Ctrl-U support on FAFT

We are going to implement a DevBootUSB test which requires sending Ctrl-U
to DUT. We only send Ctrl-U on the devices which either use Chrome EC or
support external keyboards.

BUG=chromium-os:35255
TEST=After merging the DevBootUSB test CL, run:
run_remote_tests.sh --board daisy --remote dut firmware_DevBootUSB

Change-Id: I2e2d82f2b6b1f017239ac8865173027621043ab2
Reviewed-on: https://gerrit.chromium.org/gerrit/35551
Reviewed-by: Vic Yang <victoryang@chromium.org>
Reviewed-by: Mike Truty <truty@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
2 files changed