ASoC: mikroe-proto: dt-bindings: add DT bindings for PROTO board

DT binding documentation for this new ASoC driver.

Signed-off-by: Codrin Ciubotariu <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/mikroe,mikroe-proto.txt

···
+Mikroe-PROTO audio board
+
+Required properties:
+  - compatible: "mikroe,mikroe-proto"
+  - dai-format: Must be "i2s".
+  - i2s-controller: The phandle of the I2S controller.
+  - audio-codec: The phandle of the WM8731 audio codec.
+Optional properties:
+  - model: The user-visible name of this sound complex.
+  - bitclock-master: Indicates dai-link bit clock master; for details see simple-card.txt (1).
+  - frame-master: Indicates dai-link frame master; for details see simple-card.txt (1).
+
+(1) : There must be the same master for both bit and frame clocks.
+
+Example:
+	sound {
+		compatible = "mikroe,mikroe-proto";
+		model = "wm8731 @ sama5d2_xplained";
+		i2s-controller = <&i2s0>;
+		audio-codec = <&wm8731>;
+		dai-format = "i2s";
+        };
+};

Documentation/devicetree/bindings/vendor-prefixes.txt

···
 microchip	Microchip Technology Inc.
 microcrystal	Micro Crystal AG
 micron	Micron Technology Inc.
+mikroe		MikroElektronika d.o.o.
 minix	MINIX Technology Ltd.
 miramems	MiraMEMS Sensing Technology Co., Ltd.
 mitsubishi	Mitsubishi Electric Corporation