Currently the only implementers of ARI is SR-IOV devices, and they
behave similar. Share the ARI next function number.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Ani Sinha <anisinha@redhat.com>
Message-Id: <20230710153838.33917-2-akihiko.odaki@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>