Input: i8042 - add firmware_id support

Fill in the new serio firmware_id sysfs attribute for pnp instantiated
8042 serio ports.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>