drm/msm/sde: fix programming problem causing mdp hangs

Current driver setup the left and right bit for
source split pipes, however, the dirty flag to
actually program this bit in the hw is missing
when the rect info is updated. Fix this issue by
making sure that any update in the rect also updates
the hw configuration for the left/right.

Change-Id: I5547737bc146800ffa901cfb74317e4fdccc9fb0
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>