cmhw: Add stubs for SRE support

 * Add support for Sunlight Readability Enhancement, aka Facemelt Mode.
 * Optional dependency on adaptive backlight support, which is required
   in all current implementations.

Change-Id: Id25bb5fd384f3935383a5c7f5795ce17afc73b00
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_frameworks_opt_hardware into temp