dt-bindings: gnss: add mediatek binding

Add binding for Mediatek-based GNSS receivers.
Signed-off-by: Loys Ollivier <lollivier@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
[ johan: rename backup supply ]
Signed-off-by: Johan Hovold <johan@kernel.org>

Documentation/devicetree/bindings/gnss/mediatek.txt

+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>;
+	};
+};