ARM: dts: rockchip: Add SPDIF optical out on Radxa Rock

This enables the SPDIF optical audio output on the Radxa Rock
Signed-off-by: NSjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3188-radxarock.dts

@@ -90,6 +90,21 @@
 		};
 	};
 
+	sound {
+		compatible = "simple-audio-card";
+		simple-audio-card,name = "SPDIF";
+
+		simple-audio-card,dai-link@1 {  /* S/PDIF - S/PDIF */
+			cpu { sound-dai = <&spdif>; };
+			codec { sound-dai = <&spdif_out>; };
+		};
+	};
+
+	spdif_out: spdif-out {
+		compatible = "linux,spdif-dit";
+		#sound-dai-cells = <0>;
+	};
+
 	ir_recv: gpio-ir-receiver {
 		compatible = "gpio-ir-receiver";
 		gpios = <&gpio0 10 1>;
@@ -345,6 +360,10 @@
 	};
 };
 
+&spdif {
+	status = "okay";
+};
+
 &uart0 {
 	status = "okay";
 };