drm/amd/display: Disable plane right after disconnected

HDR display playing video underflow is observed when switching
to full screen due to program a lower watermark right after unlock otg.

Instead of disable plane in next flip coming, if there is a
plane disconnected, after otg unlock wait for mpcc idle and disable
the plane, then program watermark. So there is enough warter mark to make
sure current frame data pass through.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>