Fixed Voltage regulators

Required properties:
- compatible: Must be "regulator-fixed";

Optional properties:
- gpio: gpio to use for enable control
- startup-delay-us: startup time in microseconds
- enable-active-high: Polarity of GPIO is Active high
If this property is missing, the default assumed is Active low.
- gpio-open-drain: GPIO is open drain type.
  If this property is missing then default assumption is false.

Any property defined as part of the core regulator
binding, defined in regulator.txt, can also be used.
However a fixed voltage regulator is expected to have the
regulator-min-microvolt and regulator-max-microvolt
to be the same.

Example:

	abc: fixedregulator@0 {
		compatible = "regulator-fixed";
		regulator-name = "fixed-supply";
		regulator-min-microvolt = <1800000>;
		regulator-max-microvolt = <1800000>;
		gpio = <&gpio1 16 0>;
		startup-delay-us = <70000>;
		enable-active-high;
		regulator-boot-on;
		gpio-open-drain;
	};