drm: msm: sde: Centralize last command logic for SB DMA

The original SB DMA last command logic results in multi
feature sets being applied across different frames. Update
the SB DMA logic to do a single last command per CTL path
to ensure all features using SB DMA can get applied in the
same frame.

Change-Id: Ida837765c0f018b0e03afb0a33ece625a0df81eb
Signed-off-by: Christopher Braga <cbraga@codeaurora.org>