drm/amdgpu/vcn: Add vcn/vcn1 in white list to load its firmware under sriov

Previously since vcn0/vcn1 are not enabled, loading firmware
is skipped. Now add firmware loading back since vcn0/vcn1
has already been enabled on sriov

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jane Jian <Jane.Jian@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>