virtio: add virtio 1.0 feature bit

Based on original patches by Rusty Russell, Thomas Huth
and Cornelia Huck.

Note: at this time, we do not negotiate this feature bit
in core, drivers have to declare VERSION_1 support explicitly.

For this reason we treat this bit as a device bit
and not as a transport bit for now.

After all drivers are converted, we will be able to
move VERSION_1 to core and drop it from all drivers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>