iio: sensorhub: Add sensorhub bindings

Add sensorhub bindings for sensorhub on Galaxy Gear 2.
Signed-off-by: NKarol Wrona <k.wrona@samsung.com>
Acked-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/sensorhub.txt

+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>;
+	};