HID: apple: Properly handle function keys on Keychron keyboards

Keychron's C-series and K-series of keyboards copy the vendor and
product IDs of an Apple keyboard, but only behave like that device when
set to "Mac" mode. In "Windows" mode, the Fn key doesn't generate a
scancode, so it's impossible to use the F1-F12 keys when fnmode is set
to its default value of 1.

To fix this, make fnmode default to the new value of 3, which behaves
like fnmode=2 for Keychron keyboards and like fnmode=1 for actual Apple
keyboards. This way, Keychron devices are fully usable in both "Windows"
and "Mac" modes, while behavior is unchanged for everything else.

Signed-off-by: Bryan Cain <bryancain3@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>