disp: msm: add dirty fb support

This is refactored from the upstream commit <b9fc5e01d>
("drm: Add helper to implement legacy dirtyfb").

The difference from the original commit is that full
screen update is always used to simplify the solution
no matter what the dirty region is, because msm-4.19
doesn't have fb_damage_clips support.

Change-Id: I0b534585321fde098d66cea0c51c7fc146218bd0
Signed-off-by: Ray Zhang <rayz@codeaurora.org>