msm_fb: display: add checking y direction for alpha drop

Alpha is dropped when scaling with non repeat pixel method.
Both x and y direction of scaling need to be cehcked for
alpha dropped.

Change-Id: Iba0df5a85011f179199c13ffdebac911e5c14c3c
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
msm_fb: display: Add alpha enable check in blend

FIR and M/N scalar when used for downscaling, drops
alpha channel of the given layer. To notify this, alpha_drop flag
is updated accordingly. This flag need not be checked for layers
with no alpha plane. In some scenarios alpha_drop may get enabled
for the layers with no alpha plane and cause issues realted to blend
composition of layers. Check for setting alpha_drop only if source
ayer has alpha plane.

Change-Id: Ie64b30c045a78d0d68eb9efacc76902afae7850d
Signed-off-by: Mayank Chopra <makchopra@codeaurora.org>
Merge in samsung changes