Forward-port surface dithering from CM10.1

This allows the use of 16-bit color displays without excessive color
banding; behavior can be controlled by the persist.sys.use_dithering
property.

This is a straight forward port of http://review.cyanogenmod.org/35240
for CM10.2.

Change-Id: Icb469b9cb4beb686516c60bb576dbd0a73f505e0