Disable use of YUV overlay hardware in the OMAP3 HWC

Using YUV overlays causes rendering glitches and display sync loss
when playing back certain videos, so disable their use.  (It's unclear
at this point whether this is a limitation of the hardware or a driver
bug.)

Change-Id: Ia3d8fb7aadf04feaa01cbea29962e76e224052cd