Add support for external dock batteries

Allows the external battery status to be read via framework.

Change-Id: I1340071cecab8f1733e58e4f3ba0d304f861f311

Conflicts:

	core/java/android/os/BatteryManager.java
	core/res/res/values/config.xml
	core/res/res/values/symbols.xml
	services/jni/com_android_server_BatteryService.cpp
Bring support for DockBattery

* Fix build for asus tf300t and tf700t
Signed-off-by: iGio90 <giovanni.rocca.90@gmail.com>