arm64: dts: renesas: v3msk: add EtherAVB support

Define the V3M Starter Kit board dependent part of the EtherAVB
device node.

Based on the original (and large) patch by Vladimir Barinov.
Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a77970-v3msk.dts

@@ -31,6 +31,17 @@ memory@48000000 {
 	};
 };
 
+&avb {
+	renesas,no-ether-link;
+	phy-handle = <&phy0>;
+	status = "okay";
+
+	phy0: ethernet-phy@0 {
+		rxc-skew-ps = <1500>;
+		reg = <0>;
+	};
+};
+
 &extal_clk {
 	clock-frequency = <16666666>;
 };