drm/msm/sde: Expand sspp lut_dma buf for multi-rect use cases

Currently lut_dma allocates one buffer for each SSPP feature per pipe.
This change expands the sspp_buf storage for each SSPP feature per
rect instead of per pipe.

Change-Id: Id9a6b90c996c516ab0e8c6eb16f1ff1231b9c900
Signed-off-by: Ping Li <pingli@codeaurora.org>