dm: button: add support for linux_code in button-gpio.c driver

Linux event code must be used in input devices, using buttons.

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/button/button-uclass.c

@@ -38,6 +38,16 @@ enum button_state_t button_get_state(struct udevice *dev)
 	return ops->get_state(dev);
 }
 
+int button_get_code(struct udevice *dev)
+{
+	struct button_ops *ops = button_get_ops(dev);
+
+	if (!ops->get_code)
+		return -ENOSYS;
+
+	return ops->get_code(dev);
+}
+
 UCLASS_DRIVER(button) = {
 	.id		= UCLASS_BUTTON,
 	.name		= "button",