arm64: dts: rockchip: add SPDIF node for rk3399-rockpro64

This patch adds 'disabled' SPDIF sound node and related settings
for rk3399-rockpro64.

There are 2 reasons:
  - All RK3399 dma-bus channels have been already used by I2S0/1/2
  - RockPro64 does not have SPDIF optical nor coaxial connector,
    just have 3pins
Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Link: https://lore.kernel.org/r/20200810091619.3170534-1-katsuhiro@katsuster.netSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rockpro64.dtsi

@@ -76,6 +76,23 @@ sound {
 		dais = <&i2s1_p0>;
 	};
 
+	sound-dit {
+		compatible = "audio-graph-card";
+		label = "rockchip,rk3399";
+		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: vcc12v-dcin {
 		compatible = "regulator-fixed";
 		regulator-name = "vcc12v_dcin";
@@ -698,6 +715,16 @@ &sdhci {
 	status = "okay";
 };
 
+&spdif {
+	pinctrl-0 = <&spdif_bus_1>;
+
+	spdif_p0: port {
+		spdif_p0_0: endpoint {
+			remote-endpoint = <&dit_p0_0>;
+		};
+	};
+};
+
 &spi1 {
 	status = "okay";