ASoC: samsung: Document DT bindings for Midas sound subsystem

This patch adds documentation of DT biding for the Midas sound complex.
Partially based on the *txt version by Simon Shields <simon@lineageos.org>.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200728131111.14334-1-s.nawrocki@samsung.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/samsung,midas-audio.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/samsung,midas-audio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Samsung Midas audio complex with WM1811 codec
+
+maintainers:
+  - Sylwester Nawrocki <s.nawrocki@samsung.com>
+
+properties:
+  compatible:
+    const: samsung,midas-audio
+
+  model:
+    $ref: /schemas/types.yaml#/definitions/string
+    description: The user-visible name of this sound complex.
+
+  cpu:
+    type: object
+    properties:
+      sound-dai:
+        $ref: /schemas/types.yaml#/definitions/phandle
+        description: phandle to the I2S controller
+    required:
+      - sound-dai
+
+  codec:
+    type: object
+    properties:
+      sound-dai:
+        $ref: /schemas/types.yaml#/definitions/phandle
+        description: phandle to the WM1811 CODEC
+    required:
+      - sound-dai
+
+  samsung,audio-routing:
+    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
+    description: |
+      List of the connections between audio components; each entry is
+      a pair of strings, the first being the connection's sink, the second
+      being the connection's source; valid names for sources and sinks are
+      the WM1811's pins (as documented in its binding), and the jacks
+      on the board: HP, SPK, Main Mic, Sub Mic, Headset Mic.
+
+  mic-bias-supply:
+    description: Supply for the micbias on the Main microphone
+
+  submic-bias-supply:
+    description: Supply for the micbias on the Sub microphone
+
+  fm-sel-gpios:
+    description: GPIO pin for FM selection
+
+  lineout-sel-gpios:
+    description: GPIO pin for line out selection
+
+required:
+  - compatible
+  - model
+  - cpu
+  - codec
+  - samsung,audio-routing
+  - mic-bias-supply
+  - submic-bias-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    sound {
+        compatible = "samsung,midas-audio";
+        model = "Midas";
+
+        fm-sel-gpios = <&gpaa0 3 GPIO_ACTIVE_HIGH>;
+
+        mic-bias-supply = <&mic_bias_reg>;
+        submic-bias-supply = <&submic_bias_reg>;
+
+        samsung,audio-routing =
+                "HP", "HPOUT1L",
+                "HP", "HPOUT1R",
+
+                "SPK", "SPKOUTLN",
+                "SPK", "SPKOUTLP",
+                "SPK", "SPKOUTRN",
+                "SPK", "SPKOUTRP",
+
+                "RCV", "HPOUT2N",
+                "RCV", "HPOUT2P",
+
+                "IN1LP", "Main Mic",
+                "IN1LN", "Main Mic",
+                "IN1RP", "Sub Mic",
+                "IN1LP", "Sub Mic";
+
+        cpu {
+            sound-dai = <&i2s0>;
+        };
+
+        codec {
+            sound-dai = <&wm1811>;
+        };
+
+    };