drm/msm/sde: avoid programming same plane source address

This change adds a check to the plane's pipe programming to
avoid writing the source address registers if the new values
are the same as what was written before. This avoids clutter
on the register logs and reduces the register programming
traffic slightly for those situations.

Change-Id: If9c17f14d68e3e82ea37edaf4bb5d7c8cf4eb46e
Signed-off-by: Clarence Ip <cip@codeaurora.org>