virtio: increase the queue limit to 1024

Increase the queue limit to 1024. But virtio-ccw and s390-virtio won't
support this, this is done through failing device_plugged() for those
two transports if the number of virtqueues is greater than 64.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
