dt-bindings: pwm: Add STM32 bindings

STMicroelectronics STM32 Timers PWM bindings

Must be a sub-node of an STM32 Timers device tree node.

See ../mfd/stm32-timers.txt for details about the parent node.

Required parameters:

- compatible:		Must be "st,stm32-pwm".

- pinctrl-names: 	Set to "default".

- pinctrl-0: 		List of phandles pointing to pin configuration nodes for PWM module.

			For Pinctrl properties see ../pinctrl/pinctrl-bindings.txt

Optional parameters:

- st,breakinput:	One or two <index level filter> to describe break input configurations.

			"index" indicates on which break input (0 or 1) the configuration

			should be applied.

			"level" gives the active level (0=low or 1=high) of the input signal

			for this configuration.

			"filter" gives the filtering value to be applied.

Example:

	timers@40010000 {

		#address-cells = <1>;

		#size-cells = <0>;

		compatible = "st,stm32-timers";

		reg = <0x40010000 0x400>;

		clocks = <&rcc 0 160>;

		clock-names = "clk_int";

		pwm {

			compatible = "st,stm32-pwm";

			pinctrl-0	= <&pwm1_pins>;

			pinctrl-names	= "default";

			st,breakinput = <0 1 5>;

		};

	};