drm/msm/sde: back off plane state changes in continuous splash

In current SDE driver, during continuous splash, drm plane state is
updated with crtc object of the corresponding display. Such changes
to drm plane state with in the driver is causing commit failures in
legacy commit path and pm resume case. This change avoids modifying
drm plane state directly in SDE driver.

Change-Id: Ie905c60ff0e6e547528371ef47f3f81f9cd95e29
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>