hwc: Configure MDP with updated content attributes of PTOR layers

Since there is no content underneath a PTOR layer, all overlapped
contents have been composed by Copybit on render buffer. So for a
PTOR layer, we can set blending to HWC_BLENDING_NONE and planeAlpha
to 0xFF. And the transform for the PTOR layer should be set to 0 to
avoid MDP flipping again.

Change-Id: I26fec26dcde4d9b0b62f94107a013d82074628b5