drm/amd/display: Fix wrong z-order when updating overlay planes

drm/amd/display: Fix wrong z-order when updating overlay planes

[Why]
If a commit updates an overlay plane via the legacy plane IOCTL
then the only plane in the state will be the overlay plane.

Overlay planes need to be added first to the DC context, but in the
scenario above the plane will be added last. This will result in wrong
z-order during rendering.

[How]
If any non-cursor plane has been updated then the rest of the
non-cursor planes should be added to the CRTC state.

The cursor plane doesn't need to be included for stream updates and
locking it will cause performance issues. It should be ignored.

DC requires that the surface count passed during stream updates
be the number of surfaces currently on the stream to enable fast
updates. This previously wasn't the case without this patch, so this
also allows this optimization to occur.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>