Enable UART capturing on EC interface

We want to enable the UART capturing on EC interface such that we can record
the UART output for the debug purpose.

On Link, set 'dut-control ec_uart_capture:on'
and check 'dut-control ec_uart_stream' output the EC UART results.
More complete tests refer to the FAFT change.

Change-Id: I9f4b9a409d1763eae99b9507384d2ab6516fb99f
Reviewed-on: https://gerrit.chromium.org/gerrit/55762
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Commit-Queue: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
3 files changed