ramips: move compatible for Ubiquiti Edgerouter X to DTS file

So far, the compatible for the Ubiquiti Edgerouter X has been
defined in the DTSI file and inherited for the edgerouterx.dts,
but overwritten for the edgerouterx-sfp.dts. In contrast, the
model was stored in the DTS file in both cases.

To resolve this somewhat confusing situation, move the compatible
with the device name for edgerouterx to the DTS file as well.

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

target/linux/ramips/dts/mt7621_ubiquiti_edgerouterx.dts

@@ -4,4 +4,5 @@
 
 / {
 	model = "UBNT-ERX";
+	compatible = "ubiquiti,edgerouterx", "mediatek,mt7621-soc";
 };

target/linux/ramips/dts/mt7621_ubiquiti_edgerouterx.dtsi

@@ -4,8 +4,6 @@
 #include <dt-bindings/input/input.h>
 
 / {
-	compatible = "ubiquiti,edgerouterx", "mediatek,mt7621-soc";
-
 	aliases {
 		label-mac-device = &ethernet;
 	};