virtio dataplane: adapt dataplane for virtio Version 1

Let dataplane allocate different region for the desc/avail/used
ring regions.
Take VIRTIO_RING_F_EVENT_IDX into account to increase the used/avail
rings accordingly.

[Fix 32-bit builds by changing 16lx format specifier to HWADDR_PRIx.
--Stefan]

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Message-id: 1441625636-23773-1-git-send-email-pmorel@linux.vnet.ibm.com
(changed __virtio16 into uint16_t,
 map descriptor table and available ring read-only)
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>