gpio: dt-bindings: add brcm,bcm6345-gpio bindings

Bindings for the Broadcom's brcm,bcm6345-gpio memory-mapped GPIO controllers.

These bindings can be used on any BCM63xx SoC. However, BCM6338 and BCM6345

are the only ones which don't need a pinctrl driver.

BCM6338 have 8-bit data and dirout registers, where GPIO state can be read

and/or written, and the direction changed from input to output.

BCM6345 have 16-bit data and dirout registers, where GPIO state can be read

and/or written, and the direction changed from input to output.

Required properties:

	- compatible: should be "brcm,bcm6345-gpio"

	- reg-names: must contain

		"dat" - data register

		"dirout" - direction (output) register

	- reg: address + size pairs describing the GPIO register sets;

		order must correspond with the order of entries in reg-names

	- #gpio-cells: must be set to 2. The first cell is the pin number and

			the second cell is used to specify the gpio polarity:

			0 = active high

			1 = active low

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

Optional properties:

	- native-endian: use native endian memory.

Examples:

	- BCM6338:

	gpio: gpio-controller@fffe0407 {

		compatible = "brcm,bcm6345-gpio";

		reg-names = "dirout", "dat";

		reg = <0xfffe0407 1>, <0xfffe040f 1>;

		#gpio-cells = <2>;

		gpio-controller;

	};

	- BCM6345:

	gpio: gpio-controller@fffe0406 {

		compatible = "brcm,bcm6345-gpio";

		reg-names = "dirout", "dat";

		reg = <0xfffe0406 2>, <0xfffe040a 2>;

		native-endian;

		#gpio-cells = <2>;

		gpio-controller;

	};