drm/msm/sde: add drm property for multirect mode

Since SDE DRM client is responsible for clock bandwidth
calculation and voting, the client must always be in
sync with the multirect mode programmed to hardware
in order to honor the vote.  This patch allows the
client to select the desired mode. It will fallback
to sde driver multirect mode selection if client
does not set property but uses the multirect plane.

Change-Id: I33ada26b5d0aa8ecffbb7e90dc345d57fb4a74e0
Signed-off-by: Steve Cohen <cohens@codeaurora.org>
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>