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: I8b61d0e754b7eadd1b6371e1d73fb9fe2219a8d1
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>