vhost: introduce new VhostOps vhost_force_iommu

This patch introduces new VhostOps vhost_force_iommu callback
to force enable features bit VIRTIO_F_IOMMU_PLATFORM.

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20200701145538.22333-11-lulu@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

include/hw/virtio/vhost-backend.h

@@ -121,6 +121,8 @@ typedef int (*vhost_vq_get_addr_op)(struct vhost_dev *dev,
 
 typedef int (*vhost_get_device_id_op)(struct vhost_dev *dev, uint32_t *dev_id);
 
+typedef bool (*vhost_force_iommu_op)(struct vhost_dev *dev);
+
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_backend_init vhost_backend_init;
@@ -164,6 +166,7 @@ typedef struct VhostOps {
     vhost_dev_start_op vhost_dev_start;
     vhost_vq_get_addr_op  vhost_vq_get_addr;
     vhost_get_device_id_op vhost_get_device_id;
+    vhost_force_iommu_op vhost_force_iommu;
 } VhostOps;
 
 extern const VhostOps user_ops;