u-blox GNSS Receiver DT binding

The u-blox GNSS receivers can use UART, DDC (I2C), SPI and USB interfaces.

Please see Documentation/devicetree/bindings/gnss/gnss.txt for generic
properties.

Required properties:

- compatible	: Must be one of

			"u-blox,neo-6m"
			"u-blox,neo-8"
			"u-blox,neo-m8"

- vcc-supply	: Main voltage regulator

Required properties (DDC):
- reg		: DDC (I2C) slave address

Required properties (SPI):
- reg		: SPI chip select address

Required properties (USB):
- reg		: Number of the USB hub port or the USB host-controller port
                  to which this device is attached

Optional properties:

- timepulse-gpios	: Time pulse GPIO
- u-blox,extint-gpios	: GPIO connected to the "external interrupt" input pin
- v-bckp-supply	: Backup voltage regulator

Example:

serial@1234 {
	compatible = "ns16550a";

	gnss {
		compatible = "u-blox,neo-8";

		v-bckp-supply = <&gnss_v_bckp_reg>;
		vcc-supply = <&gnss_vcc_reg>;
	};
};