drm/msm/sde: Add color processing support for dual dsi panel

For dual dsi panel configuration, two dspp's can be used. When two
dspp's are used the color processing driver needs to ensure that reg dma
programming is done for each dspp. Driver needs to set the last command
flag for the current commit. Change adds support for dual dspp support
for color processing through reg dma.

Change-Id: Idca82c110bcf3e736f4bb3dde11d60f904054c8d
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>