drm/amd/display: Avoid DPMS-on for phantom stream

drm/amd/display: Avoid DPMS-on for phantom stream

[Why & How]
Calling dc_update_planes_and_stream separately for stream and its
phantom stream causes a NULL pointer dereference, since the phantom is
destroyed on the first call.

Skip the call for phantom streams.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>