Forward-port surface dithering from CM10

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

Incorporates http://review.cyanogenmod.org/19532 from CM10 as well as
code removed in upstream commit 1b03149.

Change-Id: I290ca4ed4787dc81ac756d9af92cd6a690865a08
SurfaceFlinger: Removal of NO_RGBX_8888 flag for OMAP3

Removing this will allow color format of surface to be set for RGBX8888
that can improve performance for 32 bit framebuffer.

Tested on Nook Color with CM10
TI's commit can be found here:
review.omapzoom.org/#/c/21374/3

This will also remove the need to have BOARD_NO_RGBX_8888 := true
in the BoardConfig.mk

Change-Id: Ibc6e56c992a6433bc8688d88471d4feb9084278c