hdctools: ec: Add controls to issue EC UART commands and to get its results.

Originally FAFT directly controls the UART to send EC commands. However, we
can't do it in Autotest lab. Since the servo board is not connected to the
autoserv machine. Servod should suppport these similar functions.

So three new controls are added, on the devices which have Chrome EC.
 - ec_uart_timeout:
       Timeout value for waiting EC UART response of issuing an EC command.
 - ec_uart_regexp:
       The regular expression to match the response of EC command.
 - ec_uart_cmd:
       Set: To send the command to EC UART. Its response is matched using the
            regular expression of ec_uart_regexp.
       Get: To obtain the matched results of the latest EC command.

BUG=chromium-os:34787
TEST=manaul, with the changes on Autotest side.
$ run_remote_tests.sh --remote $DUT suite:faft_ec

Change-Id: I620edc1dbdc02595a45772dbafa0d04914b2ed1b
Reviewed-on: https://gerrit.chromium.org/gerrit/34608
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
3 files changed