virtio: Define feature bit for administration virtqueue

Introduce VIRTIO_F_ADMIN_VQ which is used for administration virtqueue
support.

Signed-off-by: Feng Liu <feliu@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20231219093247.170936-2-yishaih@nvidia.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>