msm: display: non-blocking for overlay update

Display commit will work as overlay commit when
MDP_DISPLAY_COMMIT_OVERLAY flag is set. It will be
non-blocking if wait_for_finish is false.

Signed-off-by: Ken Zhang <kenz@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>
Change-Id: Ibd143dbfcd2fdd7a8fab3038c5af4e2fbc9ea198