drm/msm: wait fence complete before flip

In async commit case, driver needs to always wait for input fence
before triggering the complete_commit path. Otherwise, there could
be tearing since GPU hasn't finished the composition rendering.

Change-Id: I73a54f5811fdcf8639618ce3cacf4cbaa00b406c
Signed-off-by: Felix Xiong <xayang@codeaurora.org>
Signed-off-by: Jin Li <jinl@codeaurora.org>