jflte: add back button backlight support

Change-Id: Ia517bce814936ba103f7c104b7abf4f9f5a740f5

Conflicts:
	overlay/frameworks/base/core/res/res/values/config.xml
jflte: enable flip cover support

related: http://review.cyanogenmod.org/#/c/68621/

Change-Id: Ieb1ddf9d1c0bdac73541394883d12383c8d6d398

Conflicts:
	BoardConfig.mk
	device.mk