recovery: Add fast factory boot mode (FFBM) read

FFBM is needed to start the system in native Android to shorten boot time
in case of factory testing. FFBM mode representation is string of the type
"ffbm-xx" where xx is number that denotes the FFBM submode.
LK reads that string from the misc partition

Change-Id: I1f93a7c60aa60493c4a277dc4979ebb5120b57b7
2 files changed