Binding for GPIO Gas Gauge

Required properties:
 - compatible: "gpio-gas-gauge"
 - gpios: GPIO which will change value to signal when the power is low and
          the system should shutdown. This GPIO should include flags to
          specify if the GPIO is active low or not. In this case, active low
          would mean that the GPIO would go 0->1 when the power is low.

Optional properties:
 - supply-name: This is a string which can be passed through to use as the
                name of the power supply. It defaults to gpio-gas-gauge.

Example:

gpio-gas-gauge {
	compatible = "gpio-gas-gauge";
	gpios = <TEGRA_GPIO(D, 3) 0>;
	supply-name = "GPIO_gas_gage";
	status = "okay";
};