Binding for the LTC2952 PowerPath controller

This chip is used to externally trigger a system shut down. Once the trigger has
been sent, the chip's watchdog has to be reset to gracefully shut down.
A full powerdown can be triggered via the kill signal.

Required properties:

- compatible:		Must contain: "lltc,ltc2952"
- watchdog-gpios:	phandle + gpio-specifier for the GPIO connected to the
			chip's watchdog line
- kill-gpios:		phandle + gpio-specifier for the GPIO connected to the
			chip's kill line

Optional properties:
- trigger-gpios:	phandle + gpio-specifier for the GPIO connected to the
			chip's trigger line. If this property is not set, the
			trigger function is ignored and the chip is kept alive
			until an explicit kill signal is received
- trigger-delay-ms	The number of milliseconds to wait after trigger line
			assertion before executing shut down procedure.
			The default is 2500ms.

Example:

ltc2952 {
	compatible = "lltc,ltc2952";

	trigger-gpios = <&gpio0 1 GPIO_ACTIVE_LOW>;
	trigger-delay-ms = <2000>;
	watchdog-gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
	kill-gpios = <&gpio0 2 GPIO_ACTIVE_LOW>;
};