libgralloc-compat: Fix YCrCb_420_SP pixel format for hammerhead

Change-Id: I896517bd2a521c551ef3ae27face2bd030db3026
hwc: Reset ROI for all the prepare calls.

Partial update ROI needs to be reset at the beginning of every
frame even when we don't have any application layers.

Change-Id: Ib4b604dfa9b589e59150ecc66f48a396f0b37af5