HID: apple_fn_keys F5 and F6

In drivers/hid/hid-input.c, the apple_fn_keys translation table
contains no entries for the F5 and F6 keys. This patch maps the F5 and
F6 keys to KBDILLUMDOWN and KBDILLUMUP, respektively, which make them
work as keyboard backlight control keys.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>