Input: HID - add support for fn key on Apple PowerBooks

This patch implements support for the fn key on Apple PowerBooks using
USB based keyboards and makes them behave like their ADB counterparts.

Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>
Acked-by: Rene Nussbaumer <linux-kernel@killerfox.forkbomb.ch>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>