msm: mdss: implement frame events notification

Allow for async frame events notifications to be done when frames are
flushed (new frame can be programmed) and frame is done (new frame can
be displayed). This allows the sync fences to be signaled in a separate
context from the display thread so that more commits can be queued.
This leads to better performance.

Change-Id: I0952f3f0ea9273a92c74fa42cd3ca9c6f9d042f3
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>