video: fbdev: atmel_lcdfb: drop AVR and platform_data support

Make the driver OF only as since AVR32 has been removed from the kernel,
there are only OF enabled platform using it.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>