SiRFstar-based GNSS Receiver DT binding

SiRFstar chipsets are used in GNSS-receiver modules produced by several
vendors and can use UART, SPI or I2C interfaces.

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

Required properties:

- compatible	: Must be one of

			"fastrax,uc430"
			"linx,r4"
			"wi2wi,w2sg0004"
			"wi2wi,w2sg0008i"
			"wi2wi,w2sg0084i"

- vcc-supply	: Main voltage regulator (pin name: 3V3_IN, VCC, VDD)

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

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

Optional properties:

- sirf,onoff-gpios	: GPIO used to power on and off device (pin name: ON_OFF)
- sirf,wakeup-gpios	: GPIO used to determine device power state
			  (pin name: RFPWRUP, WAKEUP)
- timepulse-gpios	: Time pulse GPIO (pin name: 1PPS, TM)

Example:

serial@1234 {
	compatible = "ns16550a";

	gnss {
		compatible = "wi2wi,w2sg0084i";

		vcc-supply = <&gnss_reg>;
		sirf,onoff-gpios = <&gpio0 16 GPIO_ACTIVE_HIGH>;
		sirf,wakeup-gpios = <&gpio0 17 GPIO_ACTIVE_HIGH>;
	};
};