dt-bindings: stm32-thermal: add binding documentation

Binding for Thermal Sensor for STMicroelectronics STM32 series of SoCs.

On STM32 SoCs, the Digital Temperature Sensor (DTS) is in charge of managing an

analog block which delivers a frequency depending on the internal SoC's

temperature. By using a reference frequency, DTS is able to provide a sample

number which can be translated into a temperature by the user.

DTS provides interrupt notification mechanism by threshold. This mechanism

offers two temperature trip points: passive and critical. The first is intended

for passive cooling notification while the second is used for over-temperature

reset.

Required parameters:

-------------------

compatible: 	Should be "st,stm32-thermal"

reg: 		This should be the physical base address and length of the

		sensor's registers.

clocks: 	Phandle of the clock used by the thermal sensor.

		  See: Documentation/devicetree/bindings/clock/clock-bindings.txt

clock-names: 	Should be "pclk" for register access clock and reference clock.

		  See: Documentation/devicetree/bindings/resource-names.txt

#thermal-sensor-cells: Should be 0. See ./thermal.txt for a description.

interrupts:	Standard way to define interrupt number.

Example:

	thermal-zones {

		cpu_thermal: cpu-thermal {

			polling-delay-passive = <0>;

			polling-delay = <0>;

			thermal-sensors = <&thermal>;

			trips {

				cpu_alert1: cpu-alert1 {

					temperature = <85000>;

					hysteresis = <0>;

					type = "passive";

				};

				cpu-crit: cpu-crit {

					temperature = <120000>;

					hysteresis = <0>;

					type = "critical";

				};

			};

			cooling-maps {

			};

		};

	};

	thermal: thermal@50028000 {

		compatible = "st,stm32-thermal";

		reg = <0x50028000 0x100>;

		clocks = <&rcc TMPSENS>;

		clock-names = "pclk";

		#thermal-sensor-cells = <0>;

		interrupts = <GIC_SPI 147 IRQ_TYPE_LEVEL_HIGH>;

	};