msm: mdss: fix the pack alignment of MDP output for RGB666 format

Currently for RGB666 format, the MDP output is set as LSB aligned
and banding artifacts are observed due to this. Set the MDP output
to be MSB aligned to avoid these artifacts and for the display
to show up fine with RGB666 format.

Change-Id: Id8b7bf03218dd0ea70ada34912afd092e239b89f
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>