LEDs connected to GPIO lines

Required properties:
- compatible : should be "gpio-leds".

Each LED is represented as a sub-node of the gpio-leds device.  Each
node's name represents the name of the corresponding LED.

LED sub-node properties:
- gpios :  Should specify the LED's GPIO, see "gpios property" in
  Documentation/devicetree/gpio.txt.  Active low LEDs should be
  indicated using flags in the GPIO specifier.
- label :  (optional) The label for this LED.  If omitted, the label is
  taken from the node name (excluding the unit address).
- linux,default-trigger :  (optional) This parameter, if present, is a
  string defining the trigger assigned to the LED.  Current triggers are:
    "backlight" - LED will act as a back-light, controlled by the framebuffer
		  system
    "default-on" - LED will turn on, but see "default-state" below
    "heartbeat" - LED "double" flashes at a load average based rate
    "ide-disk" - LED indicates disk activity
    "timer" - LED flashes at a fixed, configurable rate
- default-state:  (optional) The initial state of the LED.  Valid
  values are "on", "off", and "keep".  If the LED is already on or off
  and the default-state property is set the to same value, then no
  glitch should be produced where the LED momentarily turns off (or
  on).  The "keep" setting will keep the LED at whatever its current
  state is, without producing a glitch.  The default is off if this
  property is not present.

Examples:

leds {
	compatible = "gpio-leds";
	hdd {
		label = "IDE Activity";
		gpios = <&mcu_pio 0 1>; /* Active low */
		linux,default-trigger = "ide-disk";
	};

	fault {
		gpios = <&mcu_pio 1 0>;
		/* Keep LED on if BIOS detected hardware fault */
		default-state = "keep";
	};
};

run-control {
	compatible = "gpio-leds";
	red {
		gpios = <&mpc8572 6 0>;
		default-state = "off";
	};
	green {
		gpios = <&mpc8572 7 0>;
		default-state = "on";
	};
};
