init: add 'ffbm' action trigger when booting in factory mode

Android init process was extedned to recognize new boot mode
and start only required services for this mode. Init process will add
new action trigger 'ffbm', which will take care of rest of the
initialization process. 'ffbm' action trigger is defined in Qualcomm's
private init.rc file. It's functionality is identical with main
Android's 'boot' action triger except it doesnt add trigger actions
'core' and 'main'. Action trigger will start only minimal set of
services (media, adb, qcom-post-boot, rmt_storage) required for test
environment to operate correctly .

Change-Id: If74201f83d663e2f2932720cc3ecb494a61a854e