drm/msm/sde: Add support for dumping debug registers in reg dma

Add an ops to dump lut dma registers. This will be helpful in debugging
sde hangs.

Change-Id: I77b9ca773757c575d535b2f9362283ed319e4be6
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>
Signed-off-by: Ping Li <pingli@codeaurora.org>