drm/msm/sde: Move DSPP/SSPP color process to one location

The color processing blocks for SSPP and DSPP share the same register
programming sequences. This change moves the current DSPP and SSPP
functionality to a common location and uses the helper function for
common code.

Change-Id: I0f41453a977ba2d3b4ce12cc622706619c48280c
Signed-off-by: Benet Clark <benetc@codeaurora.org>