gpio: Add XRA1403 DTS binding documentation

GPIO Driver for XRA1403 16-BIT GPIO Expander With Reset Input from EXAR

The XRA1403 is an 16-bit GPIO expander with an SPI interface. Features available:

	- Individually programmable inputs:

		- Internal pull-up resistors

		- Polarity inversion

		- Individual interrupt enable

		- Rising edge and/or Falling edge interrupt

		- Input filter

	- Individually programmable outputs

		- Output Level Control

		- Output Three-State Control

Properties

----------

Check documentation for SPI and GPIO controllers regarding properties needed to configure the node.

	- compatible = "exar,xra1403".

	- reg - SPI id of the device.

	- gpio-controller - marks the node as gpio.

	- #gpio-cells - should be two where the first cell is the pin number

		and the second one is used for optional parameters.

Optional properties:

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

	- reset-gpios: in case available used to control the device reset line.

	- interrupt-controller - marks the node as interrupt controller.

	- #interrupt-cells - should be two and represents the number of cells

		needed to encode interrupt source.

Example

--------

	gpioxra0: gpio@2 {

		compatible = "exar,xra1403";

		reg = <2>;

		gpio-controller;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		reset-gpios = <&gpio3 6 GPIO_ACTIVE_LOW>;

		spi-max-frequency = <1000000>;

	};