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>