LegacyUSB: Add support for legacy USB implementations

Rebased for JB 4.2

 This is the 2nd commit message:

LegacyUSB: add overlay for UMS lun and use existence of lun to enable legacy USB

Ported to JB 4.2

Change-Id: Ia73a28504d2f455c5dbcba92bda50bc61f74ad31

Conflicts:
	core/res/res/values/symbols.xml