virtio-rng-s390: switch to the new API.

virtio-rng-s390: switch to the new API.

Here the virtio-rng-s390 is modified for the new API. The device
virtio-rng-s390 extends virtio-s390-device as before. It creates and
connects a virtio-rng during the init. The properties are not modified.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Message-id: 1366790881-3026-5-git-send-email-fred.konrad@greensocs.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>