Devicetree bindings for the Axentia TSE-850 audio complex

Required properties:
  - compatible: "axentia,tse850-pcm5142"
  - axentia,cpu-dai: The phandle of the cpu dai.
  - axentia,audio-codec: The phandle of the PCM5142 codec.
  - axentia,add-gpios: gpio specifier that controls the mixer.
  - axentia,loop1-gpios: gpio specifier that controls loop relays on channel 1.
  - axentia,loop2-gpios: gpio specifier that controls loop relays on channel 2.
  - axentia,ana-supply: Regulator that supplies the output amplifier. Must
    support voltages in the 2V - 20V range, in 1V steps.

The schematics explaining the gpios are as follows:

               loop1 relays
   IN1 +---o  +------------+  o---+ OUT1
            \                /
             +              +
             |   /          |
             +--o  +--.     |
             |  add   |     |
             |        V     |
             |      .---.   |
   DAC +----------->|Sum|---+
             |      '---'   |
             |              |
             +              +

   IN2 +---o--+------------+--o---+ OUT2
               loop2 relays

The 'loop1' gpio pin controlls two relays, which are either in loop position,
meaning that input and output are directly connected, or they are in mixer
position, meaning that the signal is passed through the 'Sum' mixer. Similarly
for 'loop2'.

In the above, the 'loop1' relays are inactive, thus feeding IN1 to the mixer
(if 'add' is active) and feeding the mixer output to OUT1. The 'loop2' relays
are active, short-cutting the TSE-850 from channel 2. IN1, IN2, OUT1 and OUT2
are TSE-850 connectors and DAC is the PCB name of the (filtered) output from
the PCM5142 codec.

Example:

	&ssc0 {
		#sound-dai-cells = <0>;

		status = "okay";
	};

	&i2c {
		codec: pcm5142@4c {
			compatible = "ti,pcm5142";

			reg = <0x4c>;

			AVDD-supply = <&reg_3v3>;
			DVDD-supply = <&reg_3v3>;
			CPVDD-supply = <&reg_3v3>;

			clocks = <&sck>;

			pll-in = <3>;
			pll-out = <6>;
		};
	};

	ana: ana-reg {
		compatible = "pwm-regulator";

		regulator-name = "ANA";

		pwms = <&pwm0 2 1000 PWM_POLARITY_INVERTED>;
		pwm-dutycycle-unit = <1000>;
		pwm-dutycycle-range = <100 1000>;

		regulator-min-microvolt = <2000000>;
		regulator-max-microvolt = <20000000>;
		regulator-ramp-delay = <1000>;
	};

	sound {
		compatible = "axentia,tse850-pcm5142";

		axentia,cpu-dai = <&ssc0>;
		axentia,audio-codec = <&codec>;

		axentia,add-gpios = <&pioA 8 GPIO_ACTIVE_LOW>;
		axentia,loop1-gpios = <&pioA 10 GPIO_ACTIVE_LOW>;
		axentia,loop2-gpios = <&pioA 11 GPIO_ACTIVE_LOW>;

		axentia,ana-supply = <&ana>;
	};