msm: mdss: Add plane alpha support

Clean up the blending rule to follow blend_op set from hwc.
Use modulate alpha for plane alpha when it is not 0xff.

Change-Id: Iad7217563bcae5e89fe8e50954494f6afdcb8e79
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
4 files changed