dt-bindings: mfd: Add bindings for STM32 Timers driver

STM32 Timers driver bindings

This IP provides 3 types of timer along with PWM functionality:

- advanced-control timers consist of a 16-bit auto-reload counter driven by a programmable

  prescaler, break input feature, PWM outputs and complementary PWM ouputs channels.

- general-purpose timers consist of a 16-bit or 32-bit auto-reload counter driven by a

  programmable prescaler and PWM outputs.

- basic timers consist of a 16-bit auto-reload counter driven by a programmable prescaler.

Required parameters:

- compatible: must be "st,stm32-timers"

- reg:			Physical base address and length of the controller's

			registers.

- clock-names:		Set to "int".

- clocks: 		Phandle to the clock used by the timer module.

			For Clk properties, please refer to ../clock/clock-bindings.txt

Optional parameters:

- resets:		Phandle to the parent reset controller.

			See ../reset/st,stm32-rcc.txt

Optional subnodes:

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

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

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";

		};

		timer@0 {

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

			reg = <0>;

		};

	};