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.
  see Documentation/devicetree/bindings/leds/common.txt
- retain-state-suspended: (optional) The suspend state can be retained.Such
  as charge-led gpio.
- retain-state-shutdown: (optional) Retain the state of the LED on shutdown.
  Useful in BMC systems, for example when the BMC is rebooted while the host
  remains up.
- panic-indicator : (optional)
  see Documentation/devicetree/bindings/leds/common.txt

Examples:

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

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

	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;
	};
};
