Add option for switching between UMS and MTP/PTP mode. (1/2)

This adds support for switching between UMS and MTP/PTP.
Framework part (this part) will only enable UMS if the config setting is set.
Standard is to enable UMS if the primary volume supports UMS.

Change-Id: If19ac297a0a581232cc8c1a829f6e30aa864a08f
power: Add CPU boosting interface

 * Boosts CPU using Power HAL for the given duration.
 * Duration is given in microseconds.
 * Power HAL must implement POWER_HINT_CPU_BOOST.

Change-Id: Ic79baf7e3d0f75483c2fe8a242b4c3d93368b68b

Conflicts:
	services/java/com/android/server/PowerManagerService.java
	services/jni/com_android_server_PowerManagerService.cpp
	tools/layoutlib/bridge/src/com/android/layoutlib/bridge/android/BridgePowerManager.java
Cleanup
Add CPU boosting hooks

 * Boost CPU to max during scrolling
 * Boost CPU to max on activity start/resume
 * Inspired by a patch from CodeAuora.

Change-Id: I72f2c2851b01fbceabddead03a4c3a7a0526ca61

Conflicts:
	services/java/com/android/server/am/ActivityStack.java