Wi2Wi GPS module connected through UART

Required properties:
- compatible: wi2wi,w2sg0004 or wi2wi,w2sg0084
- on-off-gpio: the GPIO that controls the module's on-off toggle input
- uart: the uart we are connected to (provides DTR for power control)

Optional properties:
- lna-suppy: an (optional) LNA regulator that is enabled together with the GPS receiver

example:

        gps_receiver: w2sg0004 {
                compatible = "wi2wi,w2sg0004";
                lna-supply = <&vsim>;	/* LNA regulator */
                on-off-gpio = <&gpio5 17 0>;	/* GPIO_145: trigger for turning on/off w2sg0004 */
                uart = <&uart1>;	/* we are a slave of uart1 */
        }
