[why]
In pipe split issue occurs when we program immediate flip while vsync flip is pending

[how]
Don't program immediate flip until flip is no longer pending
Signed-off-by: NAlvin Lee <alvin.lee2@amd.com>
Reviewed-by: NJaehyun Chung <Jaehyun.Chung@amd.com>
Acked-by: NLeo Li <sunpeng.li@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>