performance profile support

Many device trees support the recovery.perf.mode property to
set various core frequencies and online/offline mode. TWRP is
highly threaded, and support for multiple cores on many operations
dramatically recudes the time, e.g., backups, zip flashes, etc.

p2: removed user notifications

Change-Id: I957b8ca40b241c0af0471327eeb329cce1816017