[media] uvcvideo: Implement DMABUF exporter role

Now that videobuf2-vmalloc supports exporting buffers, add support for
the DMABUF exporter role by plugging in the videobuf2 ioctl helper.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/uvc/uvcvideo.h

@@ -635,6 +635,8 @@ extern int uvc_create_buffers(struct uvc_video_queue *queue,
 		struct v4l2_create_buffers *v4l2_cb);
 extern int uvc_queue_buffer(struct uvc_video_queue *queue,
 		struct v4l2_buffer *v4l2_buf);
+extern int uvc_export_buffer(struct uvc_video_queue *queue,
+		struct v4l2_exportbuffer *exp);
 extern int uvc_dequeue_buffer(struct uvc_video_queue *queue,
 		struct v4l2_buffer *v4l2_buf, int nonblocking);
 extern int uvc_queue_streamon(struct uvc_video_queue *queue,