HID: sony: Mark DS4 touchpad device as a pointer

Currently the DS4 touchpad device is neither classified as a direct
input device nor as a pointer device. It makes most sense to mark
it as a pointer device.

Signed-off-by: Roderick Colenbrander <roderick.colenbrander@sony.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>