GPIO controlled regulators

Required properties:
- compatible		: Must be "regulator-gpio".
- states		: Selection of available voltages and GPIO configs.
                          if there are no states, then use a fixed regulator

Optional properties:
- enable-gpio		: GPIO to use to enable/disable the regulator.
- gpios			: GPIO group used to control voltage.
- gpios-states		: gpios pin's initial states array. 0: LOW, 1: HIGH.
			  defualt is LOW if nothing is specified.
- startup-delay-us	: Startup time in microseconds.
- enable-active-high	: Polarity of GPIO is active high (default is low).
- regulator-type	: Specifies what is being regulated, must be either
			  "voltage" or "current", defaults to voltage.

Any property defined as part of the core regulator binding defined in
regulator.txt can also be used.

Example:

	mmciv: gpio-regulator {
		compatible = "regulator-gpio";

		regulator-name = "mmci-gpio-supply";
		regulator-min-microvolt = <1800000>;
		regulator-max-microvolt = <2600000>;
		regulator-boot-on;

		enable-gpio = <&gpio0 23 0x4>;
		gpios = <&gpio0 24 0x4
			 &gpio0 25 0x4>;
		states = <1800000 0x3
			  2200000 0x2
			  2600000 0x1
			  2900000 0x0>;

		startup-delay-us = <100000>;
		enable-active-high;
	};
