riscv: dts: sophgo: Add ethernet node

Add ethernet node for cv1800b SoC

Signed-off-by: Kongyang Liu <seashell11234455@gmail.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/dts/cv1800b-milkv-duo.dts b/arch/riscv/dts/cv1800b-milkv-duo.dts
index 94e64dd..f6ae882 100644
--- a/arch/riscv/dts/cv1800b-milkv-duo.dts
+++ b/arch/riscv/dts/cv1800b-milkv-duo.dts
@@ -29,6 +29,11 @@
 	};
 };
 
+&ethernet0 {
+	status = "okay";
+	phy-mode = "rmii";
+};
+
 &osc {
 	clock-frequency = <25000000>;
 };