iio: sensorhub: Add sensorhub bindings

Samsung Sensorhub driver

Sensorhub is a MCU which manages several sensors and also plays the role

of a virtual sensor device.

Required properties:

- compatible: "samsung,sensorhub-rinato" or "samsung,sensorhub-thermostat"

- spi-max-frequency: max SPI clock frequency

- interrupt-parent: interrupt parent

- interrupts: communication interrupt

- ap-mcu-gpios: [out] ap to sensorhub line - used during communication

- mcu-ap-gpios: [in] sensorhub to ap - used during communication

- mcu-reset-gpios: [out] sensorhub reset

Example:

	shub_spi: shub {

		compatible = "samsung,sensorhub-rinato";

		spi-max-frequency = <5000000>;

		interrupt-parent = <&gpx0>;

		interrupts = <2 0>;

		ap-mcu-gpios = <&gpx0 0 0>;

		mcu-ap-gpios = <&gpx0 4 0>;

		mcu-reset-gpios = <&gpx0 5 0>;

	};