ramips: add system LED indicators for TP-Link C20i

Use the WPS LED to indicate system status like it is done for the
TP-Link Archer C2 v1 and many other boards.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ramips/dts/mt7620a_tplink_archer-c20i.dts

@@ -7,6 +7,10 @@
 	model = "TP-Link Archer C20i";
 
 	aliases {
+		led-boot = &led_wps;
+		led-failsafe = &led_wps;
+		led-running = &led_wps;
+		led-upgrade = &led_wps;
 		label-mac-device = &ethernet;
 	};
 
@@ -25,7 +29,7 @@
 			linux,default-trigger = "usbport";
 		};
 
-		wps {
+		led_wps: wps {
 			label = "archer-c20i:blue:wps";
 			gpios = <&gpio1 15 GPIO_ACTIVE_LOW>;
 		};