ramips: remove model name from LED labels

Like in the previous patch for ath79 target, this will remove the
"devicename" from LED labels in ramips as well.

The devicename is removed in DTS files and 01_leds, consolidation
of definitions into DTSI files is done where (easily) possible,
and migration scripts are updated.

For the latter, all existing definitions were actually just
devicename migrations anyway. Therefore, those are removed and
a common migration file is created in target base-files. This is
actually another example of how the devicename removal makes things
easier.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/dts/mt7620a_planex_db-wrt01.dts

@@ -18,7 +18,7 @@
 		compatible = "gpio-leds";
 
 		led_power: power {
-			label = "db-wrt01:orange:power";
+			label = "orange:power";
 			gpios = <&gpio1 1 GPIO_ACTIVE_LOW>;
 		};
 	};