eeepc-laptop: split eeepc_backlight_exit()

eeepc_backlight_exit() was doing rfkill and input stuff, which
is a nonsense. This patch add two specific exit functions, one
for input and one for rfkill.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>