dt-bindings: mfd: Add STM32 LPTimer binding

STMicroelectronics STM32 Low-Power Timer

The STM32 Low-Power Timer (LPTIM) is a 16-bit timer that provides several

functions:

- PWM output (with programmable prescaler, configurable polarity)

- Quadrature encoder, counter

- Trigger source for STM32 ADC/DAC (LPTIM_OUT)

Required properties:

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

- reg:			Offset and length of the device's register set.

- clocks:		Phandle to the clock used by the LP Timer module.

- clock-names:		Must be "mux".

- #address-cells:	Should be '<1>'.

- #size-cells:		Should be '<0>'.

Optional subnodes:

- pwm:			See ../pwm/pwm-stm32-lp.txt

- counter:		See ../iio/timer/stm32-lptimer-cnt.txt

- trigger:		See ../iio/timer/stm32-lptimer-trigger.txt

Example:

	timer@40002400 {

		compatible = "st,stm32-lptimer";

		reg = <0x40002400 0x400>;

		clocks = <&timer_clk>;

		clock-names = "mux";

		#address-cells = <1>;

		#size-cells = <0>;

		pwm {

			compatible = "st,stm32-pwm-lp";

			pinctrl-names = "default";

			pinctrl-0 = <&lppwm1_pins>;

		};

		trigger@0 {

			compatible = "st,stm32-lptimer-trigger";

			reg = <0>;

		};

		counter {

			compatible = "st,stm32-lptimer-counter";

			pinctrl-names = "default";

			pinctrl-0 = <&lptim1_in_pins>;

		};

	};