drm: msm: sde: Fix the reg dma last command sequence

Control trigger should be sent only for last command of a frame sequence.
Currently driver is sending the trigger for each command packet which
will cause the SDE hardware to stall. Change fixes the last command
sequence.

Change-Id: Ibce3b1d42b1d5e0f8ff87b6dbcc9dd1c2f5de84c
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>