video: fbdev: omap2: remove rfbi

Equivalent of drm's commit aa61321d ("drm/omap: remove rfbi").

The RFBI driver has been marked as BROKEN and has not been
included in the kernel build for many years. Just remove it
(it can be trivially brought back from git repository if
ever needed).

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>