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>