arm64: zynqmp: Use backward compatible string for gem

Add backward compatible string for gem ("cdns,gem").

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/dts/zynqmp.dtsi b/arch/arm/dts/zynqmp.dtsi
index 854608c..dea918a 100644
--- a/arch/arm/dts/zynqmp.dtsi
+++ b/arch/arm/dts/zynqmp.dtsi
@@ -539,7 +539,7 @@
 		};
 
 		gem0: ethernet@ff0b0000 {
-			compatible = "cdns,zynqmp-gem";
+			compatible = "cdns,zynqmp-gem", "cdns,gem";
 			status = "disabled";
 			interrupt-parent = <&gic>;
 			interrupts = <0 57 4>, <0 57 4>;
@@ -552,7 +552,7 @@
 		};
 
 		gem1: ethernet@ff0c0000 {
-			compatible = "cdns,zynqmp-gem";
+			compatible = "cdns,zynqmp-gem", "cdns,gem";
 			status = "disabled";
 			interrupt-parent = <&gic>;
 			interrupts = <0 59 4>, <0 59 4>;
@@ -565,7 +565,7 @@
 		};
 
 		gem2: ethernet@ff0d0000 {
-			compatible = "cdns,zynqmp-gem";
+			compatible = "cdns,zynqmp-gem", "cdns,gem";
 			status = "disabled";
 			interrupt-parent = <&gic>;
 			interrupts = <0 61 4>, <0 61 4>;
@@ -578,7 +578,7 @@
 		};
 
 		gem3: ethernet@ff0e0000 {
-			compatible = "cdns,zynqmp-gem";
+			compatible = "cdns,zynqmp-gem", "cdns,gem";
 			status = "disabled";
 			interrupt-parent = <&gic>;
 			interrupts = <0 63 4>, <0 63 4>;