Input: wacom - add support for DTU2231 and DTU1631

Add support for the two new devices: DTU2231 and DTU1631.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/input/tablet/wacom_wac.h b/drivers/input/tablet/wacom_wac.h
index 854b920..99e1a54 100644
--- a/drivers/input/tablet/wacom_wac.h
+++ b/drivers/input/tablet/wacom_wac.h
@@ -43,6 +43,7 @@
 	WACOM_G4,
 	PTU,
 	PL,
+	DTU,
 	INTUOS,
 	INTUOS3S,
 	INTUOS3,