ramips: add missing soc compatibles to dts

Add SoC compatibles where missing.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/ramips/dts/UBNT-ER-e50.dtsi

@@ -4,7 +4,7 @@
 #include <dt-bindings/input/input.h>
 
 / {
-	compatible = "ubiquiti,edgerouterx";
+	compatible = "ubiquiti,edgerouterx", "mediatek,mt7621-soc";
 
 	memory@0 {
 		device_type = "memory";

target/linux/ramips/dts/UBNT-ERX-SFP.dts

@@ -6,7 +6,7 @@
 
 / {
 	model = "UBNT-ERX-SFP";
-	compatible = "ubiquiti,edgerouterx-sfp";
+	compatible = "ubiquiti,edgerouterx-sfp", "mediatek,mt7621-soc";
 
 	i2c-gpio {
 		compatible = "i2c-gpio";