dm: test: Add a test for the LED uclass

Add a test to confirm that we can adjust LEDs using the led_gpio driver.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/led/led_gpio.c

@@ -41,10 +41,16 @@ static int led_gpio_probe(struct udevice *dev)
 
 static int led_gpio_remove(struct udevice *dev)
 {
+	/*
+	 * The GPIO driver may have already been removed. We will need to
+	 * address this more generally.
+	 */
+#ifndef CONFIG_SANDBOX
 	struct led_gpio_priv *priv = dev_get_priv(dev);
 
 	if (dm_gpio_is_valid(&priv->gpio))
 		dm_gpio_free(dev, &priv->gpio);
+#endif
 
 	return 0;
 }