drm/amd/display: Assign stream status for FPO + Vactive cases

A new check was added to ensure FPO is not enabled when the FPO pipe has
0 planes. This requires the stream status to check the plane count, but
the stream status was not assigned for FPO + Vactive cases which leads
to FPO not be enabled always.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Relja Vojvodic <relja.vojvodic@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>