charger: Add support for non-standard charging interfaces

 * Certain devices may have multiple battery devices or broken uevent
   reporting when a power supply is disconnected.
 * Add a new BOARD_BATTERY_DEVICE_NAME to force which device to monitor.
 * Needed for galaxys2 family
   https://gerrit.omnirom.org/#/c/3979/

Change-Id: I3045bf17a4d962cc5f0e6a951472916412ac0d0d