HID: lenovo: Rename fn_lock sysfs attr handlers to make them generic

Except for a single call, there is nothing keyboard-model specific about
the cptkbd fn_lock sysfs attr handlers, rename them dropping the cptkbd
post-/pre-fix, so that they can be re-used for supporting Fn-lock on the
Thinkpad 10 ultrabook kbd.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>