leds: apu: drop superseeded apu2/3 led support

This driver only supports gpio-attached LEDs on apu1/2/3 boards,
but neither gpio's themselves, nor other gpio-attached devices
(eg. front button).

For apu2+ a newer, more complete driver exists, based on a generic
driver for the AMD SOCs gpio-controller, supporting LEDs as well
other devices. Therefore these boards don't need legacy support
from this driver anymore.

Both drivers claim the same device, so only one driver may exist
in a system, putting distros in the position to decide between
either apu2+ keys or apu1 led support.

Therefore drop the apu2+ led support from the old driver, solve
the conflict and reduce unnecessary code.

Signed-off-by: Enrico Weigelt <info@metux.net>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>