dt-bindings: gnss: add mediatek binding

Mediatek-based GNSS Receiver DT binding

Mediatek chipsets are used in GNSS-receiver modules produced by several

vendors and can use a UART interface.

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

properties.

Required properties:

- compatible	: Must be

			"globaltop,pa6h"

- vcc-supply	: Main voltage regulator (pin name: VCC)

Optional properties:

- current-speed		: Default UART baud rate

- gnss-fix-gpios	: GPIO used to determine device position fix state

			  (pin name: FIX, 3D_FIX)

- reset-gpios		: GPIO used to reset the device (pin name: RESET, NRESET)

- timepulse-gpios	: Time pulse GPIO (pin name: PPS1, 1PPS)

- vbackup-supply	: Backup voltage regulator (pin name: VBAT, VBACKUP)

Example:

serial@1234 {

	compatible = "ns16550a";

	gnss {

		compatible = "globaltop,pa6h";

		vcc-supply = <&vcc_3v3>;

	};

};