dm: led: Support "default-state" property

Add support for the device tree property "default-state". This feature
might be useful for LEDs indicating "power on" or similar states.

Note: Even with this commit gpio-leds remain in reset state. That's
because the led_gpio is not probed until DM_FLAG_ACTIVATED is set.

Signed-off-by: Patrick Bruenn <p.bruenn@beckhoff.com>

drivers/led/led_gpio.c

@@ -57,11 +57,25 @@ static int led_gpio_probe(struct udevice *dev)
 {
 	struct led_uc_plat *uc_plat = dev_get_uclass_platdata(dev);
 	struct led_gpio_priv *priv = dev_get_priv(dev);
+	const char *default_state;
+	int ret;
 
 	/* Ignore the top-level LED node */
 	if (!uc_plat->label)
 		return 0;
-	return gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
+
+	ret = gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
+	if (ret)
+		return ret;
+
+	default_state = dev_read_string(dev, "default-state");
+	if (default_state) {
+		if (!strncmp(default_state, "on", 2))
+			gpio_led_set_state(dev, LEDST_ON);
+		else if (!strncmp(default_state, "off", 3))
+			gpio_led_set_state(dev, LEDST_OFF);
+	}
+	return 0;
 }
 
 static int led_gpio_remove(struct udevice *dev)