The current display driver does not double buffer. Most GUI frameworks hand double buffing themselves (they create their own frame buffer for drawing, then copy it to the main frame buffer when needed). Therefore, the driver itself does not need to handle double buffering.
The display driver ( drivers/video/renesas/vdc5fb.c ) has partial code to support the ioctl "FBIOPUT_FRAME" which will allow you to switch between multiple frame buffers, but it requires more development.
Chris