disp: msm: sde: fix RC single region use case

Fix rounded corner single region use case where input
parameters are valid only for the region to be programmed.
Consequently, the other region must be disabled and atomic
check requirements can be relaxed.

Change-Id: I84f213f2c34f7cceb10c54bbba68fa7b0e16caf2
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>