msm_fb: display: Fix blend configuration for MDP4.1

MDP4.1 blend operation registers are not double buffered and
take effect as soon as they are configured. Configuring these
registers at any place other than between dma and vsync produce
flickers as new blend values would get applied to previous
mixer configurations. Configure blend operation registers just
after dma is over, before vsync.

Change-Id: I377c11222f7a0cd77e98e90edec6e2e1dc0c17ca
Signed-off-by: Pradeep Jilagam <pjilagam@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>
msm_fb: display: silent blending error warning message

If there had no any pipe blending stage changes, then do not
call belnding set up to avoid unnecessary warning messges.

CRs-fixed: 467556
Change-Id: I07520b3b0917375c41405e736dcb9eb8a3daddc1
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Revert "msm_fb: display: remove background invert alpha option for alpha drop pipe"

This reverts commit 0119007a18aae8a8fb43f4320509bda161da4167.

CRs-fixed: 461574
Change-Id: Ia768030ec859a4ff38549686936789413826df32
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
msm: display: 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.
Keep backward compatibility if blend_op is not set.

Change-Id: I02fd3c3c7b5ace2e6eec22b2db0284161404a0fc
Signed-off-by: Ken Zhang <kenz@codeaurora.org>