dt/bindings: Document gpio-ingenic

Ingenic jz47xx GPIO controller

That the Ingenic GPIO driver node must be a sub-node of the Ingenic pinctrl

driver node.

Required properties:

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

 - compatible: Must contain one of:

    - "ingenic,jz4740-gpio"

    - "ingenic,jz4770-gpio"

    - "ingenic,jz4780-gpio"

 - reg: The GPIO bank number.

 - interrupt-controller: Marks the device node as an interrupt controller.

 - interrupts: Interrupt specifier for the controllers interrupt.

 - #interrupt-cells: Should be 2. Refer to

   ../interrupt-controller/interrupts.txt for more details.

 - gpio-controller: Marks the device node as a GPIO controller.

 - #gpio-cells: Should be 2. The first cell is the GPIO number and the second

    cell specifies GPIO flags, as defined in <dt-bindings/gpio/gpio.h>. Only the

    GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags are supported.

 - gpio-ranges: Range of pins managed by the GPIO controller. Refer to

   'gpio.txt' in this directory for more details.

Example:

--------

&pinctrl {

	#address-cells = <1>;

	#size-cells = <0>;

	gpa: gpio@0 {

		compatible = "ingenic,jz4740-gpio";

		reg = <0>;

		gpio-controller;

		gpio-ranges = <&pinctrl 0 0 32>;

		#gpio-cells = <2>;

		interrupt-controller;

		#interrupt-cells = <2>;

		interrupt-parent = <&intc>;

		interrupts = <28>;

	};

};