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/bindings/gpio/gpio.txt.  Active low LEDs should be
  indicated using flags in the GPIO specifier.
- label :  (optional)
  see Documentation/devicetree/bindings/leds/common.txt
- linux,default-trigger :  (optional)
  see Documentation/devicetree/bindings/leds/common.txt
- 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.
- retain-state-suspended: (optional) The suspend state can be retained.Such
  as charge-led gpio.

Examples:

#include <dt-bindings/gpio/gpio.h>

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

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

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

leds {
	compatible = "gpio-leds";

	charger-led {
		gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
		linux,default-trigger = "max8903-charger-charging";
		retain-state-suspended;
	};
};
