Make applying gamma less laggy.

Applying gamma takes a while, so optimize out multiple set requests
occuring quickly after each other. Those appear e.g. when dragging the
sliders quickly.

Change-Id: I48c71b8e041679bcce932f99d198f4e6a027010a
Merge branch 'cm-10.2' of git://github.com/CyanogenMod/android_device_lge_mako into HEAD