drm/msm/sde: trigger frame done if ctl is idle

Command mode display triggers next frame without waiting
for current frame transfer complete. In this case, MDP
HW transfers two frames and generates done interrupt status
 for two frames. SW may miss one interrupt if there is a
jiffie jump during these two frame done interrupt. This patch
checks the controller idle status for posted start triggered
frame to avoid invalid pingpong timeout issue.

Change-Id: I344357f19e051ebd5ff4d5555d7d27009803f7c2
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>
Signed-off-by: Ray Zhang <rayz@codeaurora.org>
Signed-off-by: Bruce Hoo <bingchua@codeaurora.org>