Device-Tree Bindings for a PPS Signal on GPIO

These properties describe a PPS (pulse-per-second) signal connected to
a GPIO pin.

Required properties:
- compatible: should be "pps-gpio"
- gpios: one PPS GPIO in the format described by ../gpio/gpio.txt

Optional properties:
- assert-falling-edge: when present, assert is indicated by a falling edge
                       (instead of by a rising edge)
- capture-clear: when present, captures clear events (If asserts on falling
                 edge, clear events occur on rising edge or vice-versa)

Example:
	pps {
		compatible = "pps-gpio";
		gpios = <&gpio2 6 0>;

		assert-falling-edge;
	};