drm/msm/sde: fix exclusion rect control programming

Current SDE driver does not reset respective exclusion rect
enable bit if a plane is un-staged. If a VIG plane is switched
from multi-rect mode with exclusion rect to non-multirect mode,
MDSS HW expects explicit clear of REC1 exclusion rect enable.
This change updates exclusion rect control programming as per
MDSS HW expectation.

Change-Id: Icf7e27cf3ca77541eadaeec97aed50d82fed3a80
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>