drm/amd/display: Remove dangling planes on dc commit state

When disabling pipe splitting, we need to make sure we disable both
planes used.

This should be done for Linux as well.

Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@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>