Introduce a helper for registering different flavours of virtio
devices.  Convert code to use the helper, but keep only the
existing generic types.  Transitional and non-transitional device
types will be added by another patch.
Acked-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>