HID: allow disabling hard-coded ISO-layout for Apple keyboards

This patch adds a new option named "iso_layout" to the driver
"hid-apple.ko", to allow disabling of the hard-coded ISO-layout.

Disabling the hard-coded layout solves the problem that the kernel-module only
works perfectly for the english/american version of the Apple aluminum
keyboard. Other versions have swapped keys, e.g. the "<"-key  is swapped with
"^"-key on the german keyboard. There is a very long bug-entry on Launchpad to
this problem:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/214786



Signed-off-by: Stefan Glasenhardt <stefan@glasen-hardt.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>