arm64: dts: rockchip: add SPDIF node for ROCK Pi 4

Add a SPDIF audio-graph-card to ROCK Pi 4 device tree.

It's not enabled by default since all dma channels are used by
the (already) enabled i2s0/1/2 and the pin is muxed with GPIO4_C5
which might be in use already.
If enabled SPDIF_TX will be available at pin #15.
Signed-off-by: Alex Bee <knaerzche@gmail.com>
Link: https://lore.kernel.org/r/20210618181256.27992-6-knaerzche@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rock-pi-4.dtsi

@@ -42,6 +42,23 @@ sound {
 		dais = <&i2s0_p0>;
 	};
 
+	sound-dit {
+		compatible = "audio-graph-card";
+		label = "SPDIF";
+		dais = <&spdif_p0>;
+	};
+
+	spdif-dit {
+		compatible = "linux,spdif-dit";
+		#sound-dai-cells = <0>;
+
+		port {
+			dit_p0_0: endpoint {
+				remote-endpoint = <&spdif_p0_0>;
+			};
+		};
+	};
+
 	vcc12v_dcin: dc-12v {
 		compatible = "regulator-fixed";
 		regulator-name = "vcc12v_dcin";
@@ -631,6 +648,15 @@ &sdhci {
 	status = "okay";
 };
 
+&spdif {
+
+	spdif_p0: port {
+		spdif_p0_0: endpoint {
+			remote-endpoint = <&dit_p0_0>;
+		};
+	};
+};
+
 &tcphy0 {
 	status = "okay";
 };