ASoC: meson: add tohdmitx DT bindings

Add the bindings and the related documentation for the audio hdmitx
control glue of the Amlogic g12a SoC family

Signed-off-by: Jerome Brunet <[e-mail]>
Tested-by: Neil Armstrong <[e-mail]>
Tested-by: Kevin Hilman <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/amlogic,g12a-tohdmitx.txt

···
+* Amlogic HDMI Tx control glue
+
+Required properties:
+- compatible: "amlogic,g12a-tohdmitx"
+- reg: physical base address of the controller and length of memory
+       mapped region.
+- #sound-dai-cells: should be 1.
+
+Example on the S905X2 SoC:
+
+tohdmitx: audio-controller@744 {
+	compatible = "amlogic,g12a-tohdmitx";
+	reg = <0x0 0x744 0x0 0x4>;
+	#sound-dai-cells = <1>;
+};
+
+Example of an 'amlogic,axg-sound-card':
+
+sound {
+	compatible = "amlogic,axg-sound-card";
+
+[...]
+
+	dai-link-x {
+		sound-dai = <&tdmif_a>;
+		dai-format = "i2s";
+		dai-tdm-slot-tx-mask-0 = <1 1>;
+
+		codec-0 {
+			sound-dai = <&tohdmitx TOHDMITX_I2S_IN_A>;
+		};
+
+		codec-1 {
+			sound-dai = <&external_dac>;
+		};
+	};
+
+	dai-link-y {
+		sound-dai = <&tdmif_c>;
+		dai-format = "i2s";
+		dai-tdm-slot-tx-mask-0 = <1 1>;
+
+		codec {
+			sound-dai = <&tohdmitx TOHDMITX_I2S_IN_C>;
+		};
+	};
+
+	dai-link-z {
+		sound-dai = <&tohdmitx TOHDMITX_I2S_OUT>;
+
+		codec {
+			sound-dai = <&hdmi_tx>;
+		};
+	};
+};

include/dt-bindings/sound/meson-g12a-tohdmitx.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DT_MESON_G12A_TOHDMITX_H
+#define __DT_MESON_G12A_TOHDMITX_H
+
+#define TOHDMITX_I2S_IN_A	0
+#define TOHDMITX_I2S_IN_B	1
+#define TOHDMITX_I2S_IN_C	2
+#define TOHDMITX_I2S_OUT	3
+#define TOHDMITX_SPDIF_IN_A	4
+#define TOHDMITX_SPDIF_IN_B	5
+#define TOHDMITX_SPDIF_OUT	6
+
+#endif /* __DT_MESON_G12A_TOHDMITX_H */