msm: mdss: wait for dma done while entering static screen

Wait for dma done interrupt before detaching iommu and
turning off the clocks for static screen for command
mode display. Currently on 8909 we wait for 4 VSYNC and
if there is no new commit coming in then we turn off the
clocks and detach iommu. Due to any reason if DMA
transfer takes more than this much of time then the NOC
errors will be seen as we are entering static screen
while DMA is still active.

Change-Id: Idf67545734115713d4f2c278b1acd417bade3527
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>