ramips: update device tree source files

Use the GPIO dt-bindings macros and add compatible strings in the
ramips device tree source files.

Signed-off-by: L. D. Pinney <ldpinney@gmail.com>
Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/ramips/dts/NIXCORE-16M.dts

@@ -3,6 +3,7 @@
 #include "NIXCORE.dtsi"
 
 / {
+	compatible = "nixcore,x1-16m", "nixcore,x1", "ralink,rt5350-soc";
 	model = "NixcoreX1 (16M)";
 };