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

 This is the 2nd commit message:

UsbService: LegacyUSB initialize mDeviceManager sooner

Change-Id: I6730ac202167389ca55904c9db0db4c5b3eae78b

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