HID: multitouch: export a quirk for the button handling of touchpads

Instead of using the class name, we better have a specific quirk for it
so other classes can make use of it.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>