hwc/overlay: Add premultiplied alpha support.

Add premultiplied alpha belnding support while using MDP for composition.
Layers could have PMA blending which was missing from hwc1.1
This change just handles the PMA case.

Bug: 7301436
Change-Id: I7d83169831b40943b2b595723fefc3a95a177137
Signed-off-by: Iliyan Malchev <malchev@google.com>
3 files changed