msm_fb: display: consolidate overlay_commit and display_commit

This patch consolidate overlay_commit into display_commit to
support iommu buffer be used as frame buffer

Change-Id: Idc33a340b7cf199c8e2f5e7f09b901d1502fac9e
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
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