msm_fb: display: configure dsi control as free run

Configure DSI controller as free run instead of software
trigger.  At free run, DSI controller is triggered by
MDP directly when output of blending is ready. No extra
register write to trigger DSI controller is necessary.
Therefore it reduce latency during MDP kickoff.

Change-Id: I630cc47be806a8de383648aa80804b4d65210d4d
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>