msm: mdss: configure dma source when displaying new frame

Configure the dma only when there is change in format
or stride. This will avoid reconfigure of dma while
dma is active.

Change-Id: I31349df7bd5abc7dae7de64439732e978da2098a
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>