HID: wacom: generic: add vendor defined touch

Add vendor defined touch to support the second generation Intuos Pro.
Previously all generic Wacom devices used true HID to report their touch.

Signed-off-by: Aaron Skomra <aaron.skomra@wacom.com>
Reviewed-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/wacom.h b/drivers/hid/wacom.h
index 8d8fe30..0e7b840 100644
--- a/drivers/hid/wacom.h
+++ b/drivers/hid/wacom.h
@@ -219,4 +219,5 @@ enum led_brightness wacom_leds_brightness_get(struct wacom_led *led);
 struct wacom_led *wacom_led_find(struct wacom *wacom, unsigned int group,
 				 unsigned int id);
 struct wacom_led *wacom_led_next(struct wacom *wacom, struct wacom_led *cur);
+int wacom_equivalent_usage(int usage);
 #endif