Add support for Toad GPIOs in servod

The Toad cable has the FT230X GPIOx connected to a Silego part to
control the mux mode (EC/AP/EC monitor mode) and VBUS.

BUG=chrome-os-partner:17570
TEST=with a Toad cable connected, run :
"dut-control uart_mux && dut-control mode_sw:press &&
dut-control mode_sw:release && dut-control uart_mux"
and see the mux switched from EC to AP and vice-versa.

Change-Id: I21f546d18d77b50364da600d2f5723ec77276605
Reviewed-on: https://gerrit.chromium.org/gerrit/47920
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
2 files changed