mtp: cleanup, fixes and performance improvements

- use std::map instead of linked list
- read directories on demand
- fix writing zip files to storage root
- fix creating directories
- lots of minor fixes
- simplify generation of storage IDs and make them spec compliant

Change-Id: I2137c27549ddbdc58466f2e3aeda464fac70a3c5
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
Merge remote-tracking branch 'omni/android-4.4' into android-4.4