msm: display: make pan display as a non-blocking call

Schedule a workqueue, do the current job in the workqueue handler.
Block the second entry if the first one has not finished

(cherry picked from commit c760154faefd4772824cc2b032f5375f4ff1b75e)

Change-Id: I38d5487a9002d08449f865b35720adb54e158f5b
Signed-off-by: Ken Zhang <kenz@codeaurora.org>