vdpa: Add resume operation

Add a new operation to allow a vDPA device to be resumed after it has
been suspended. Trying to resume a device that wasn't suspended will
result in a no-op.

This operation is optional. If it's not implemented, the associated
backend feature bit will not be exposed. And if the feature bit is not
exposed, invoking this operation will return an error.
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Message-Id: <6e05c4b31b47f3e29cb2bd7ebd56c81f84b8f48a.1672742878.git.sebastien.boeuf@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

include/linux/vdpa.h

@@ -219,7 +219,10 @@ struct vdpa_map_file {
  * @reset:			Reset device
  *				@vdev: vdpa device
  *				Returns integer: success (0) or error (< 0)
- * @suspend:			Suspend or resume the device (optional)
+ * @suspend:			Suspend the device (optional)
+ *				@vdev: vdpa device
+ *				Returns integer: success (0) or error (< 0)
+ * @resume:			Resume the device (optional)
  *				@vdev: vdpa device
  *				Returns integer: success (0) or error (< 0)
  * @get_config_size:		Get the size of the configuration space includes
@@ -324,6 +327,7 @@ struct vdpa_config_ops {
 	void (*set_status)(struct vdpa_device *vdev, u8 status);
 	int (*reset)(struct vdpa_device *vdev);
 	int (*suspend)(struct vdpa_device *vdev);
+	int (*resume)(struct vdpa_device *vdev);
 	size_t (*get_config_size)(struct vdpa_device *vdev);
 	void (*get_config)(struct vdpa_device *vdev, unsigned int offset,
 			   void *buf, unsigned int len);