faft: Create ModeSwitcher and FwBypasser according to FAFT config

Two new FAFT configs are added:
 - mode_switcher_type: either 'physical_button_switcher' or
                       'keyboard_dev_switcher',
 - fw_bypasser_type: so far only 'ctrl_d_bypasser'

FAFT checks these configs to create proper ModeSwitcher and FwBypasser.

BUG=chrome-os-partner:39744
TEST=Ran suites faft_lv1 and faft_lv2 on Samus.

Change-Id: I6a93dc6729aec571e4fc5a0e0a4468eadcbfa771
Reviewed-on: https://chromium-review.googlesource.com/272304
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Tested-by: Tom Tam <waihong@google.com>
Commit-Queue: Tom Tam <waihong@google.com>
7 files changed