video: fbdev: radeon: Remove dead code

This is dead code since 3.15 and can be removed if not
going to be useful further.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1582042556-21555-1-git-send-email-jrdr.linux@gmail.com