msm_fb: display: add stage commit before kickoff to WFD

Since stage commit had been splited out of stage up fucnction,
it needed to be called to stage pipes into mixer befroe
kickoff mixer. Add this function into overlay writeback for WFD.

Change-Id: I11e4486d92b89a15e58531033d474b3137b5935a
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>