dt-bindings: add generic gnss binding

GNSS Receiver DT binding

This documents the binding structure and common properties for GNSS receiver

devices.

A GNSS receiver node is a node named "gnss" and typically resides on a serial

bus (e.g. UART, I2C or SPI).

Please refer to the following documents for generic properties:

	Documentation/devicetree/bindings/serial/slave-device.txt

	Documentation/devicetree/bindings/spi/spi-bus.txt

Required properties:

- compatible	: A string reflecting the vendor and specific device the node

		  represents

Optional properties:

- enable-gpios	: GPIO used to enable the device

- timepulse-gpios	: Time pulse GPIO

Example:

serial@1234 {

	compatible = "ns16550a";

	gnss {

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

		vcc-supply = <&gnss_reg>;

		timepulse-gpios = <&gpio0 16 GPIO_ACTIVE_HIGH>;

		current-speed = <4800>;

	};

};

GNSS SUBSYSTEM

M:	Johan Hovold <johan@kernel.org>

S:	Maintained

F:	Documentation/devicetree/bindings/gnss/

F:	drivers/gnss/

F:	include/linux/gnss.h