vdpa_sim: use weak barriers

vDPA simulators are software emulated device, so let's switch to use
weak barriers to avoid extra overhead in the driver.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221221062146.15356-1-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>

drivers/vdpa/vdpa_sim/vdpa_sim.c

@@ -68,7 +68,7 @@ static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
 	struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
 	uint16_t last_avail_idx = vq->vring.last_avail_idx;
 
-	vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, false,
+	vringh_init_iotlb(&vq->vring, vdpasim->features, vq->num, true,
 			  (struct vring_desc *)(uintptr_t)vq->desc_addr,
 			  (struct vring_avail *)
 			  (uintptr_t)vq->driver_addr,