Only show backlight option if hw keys disabler is "true" in device overlay

Conflicts:
	src/com/android/settings/ButtonSettings.java

Change-Id: I1bbca381fe41168ab7b23078e873dd852781ab58
Added missing lines from previous CP and also picked up to much from the commit below
https://github.com/TeamBliss-LP/android_packages_apps_Settings/commit/e4e521c4d2239fb17fa4855a4cfba767bb8ae68e
We don't use CM volume to wake settings or cursor control.

Change-Id: I64c10e3fb22ccb5778e098240532644f09162cda