* PWM beeper device tree bindings

Registers a PWM device as beeper.

Required properties:
- compatible: should be "pwm-beeper"
- pwms: phandle to the physical PWM device

Optional properties:
- amp-supply: phandle to a regulator that acts as an amplifier for the beeper
- beeper-hz:  bell frequency in Hz

Example:

beeper_amp: amplifier {
	compatible = "fixed-regulator";
	gpios = <&gpio0 1 GPIO_ACTIVE_HIGH>;
};

beeper {
	compatible = "pwm-beeper";
	pwms = <&pwm0>;
	amp-supply = <&beeper_amp>;
};