drm/amdgpu/gmc8: update MC firmware for polaris

commit a81a7c9c9ea3042ab02d66ac35def74abf091c15 upstream.

Some variants require different MC firmware images.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>