drm/msm/sde: Add reg dma programming support for vlut

If platform supports reg dma feature, dspp lut programming can be done
through axi interface. Change adds support to dynamically check for reg
dma presence and install appropriate ops during driver probe.

Change-Id: I6d9dc268d3422b80870ed6249ec086d9e3ae5c8b
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>