[media] ati_remote: migrate to the rc subsystem

The keycode mangling algorithm is kept the same, so the new external
keymap has the same values as the old static table.

[mchehab@redhat.com: Fix some bad whitespacing]
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>