settings: Add support for SRE

 * Add support for sunlight readability enhancement
 * Optionally depends on adaptive backlight, depending on HAL

Change-Id: I9ca388ffd68080f0e497edb81d5f8616c194ea1d

Conflicts:
	res/values/cm_strings.xml
	res/xml/display_settings.xml
	src/com/android/settings/DisplaySettings.java