HID: apple: Magic Keyboard 2015 FN key mapping

HID: apple: Magic Keyboard 2015 FN key mapping

The Magic Keyboard 2015 function key mapping was not present and the
default mapping was used.
While this worked for most keys, the F5 and F6 keys were sending
KEY_KBDILLUMDOWN and KEY_KBDILLUMUP; however, the keyboard is not
backlited.

Add a custom translation table for the keyboard leaving F5 and F6
unassigned to mimic the default behavior on macOS.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>