Without dt mode, device IOTLB notifier won't work since guest won't
send device IOTLB invalidation descriptor in this case. Let's fail
early instead of misbehaving silently.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Tested-by: Viktor Prutyanov <viktor@daynix.com>
Buglink: https://bugzilla.redhat.com/2156876


Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230223065924.42503-3-jasowang@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>