Austrian Microsystems AS3935 Franklin lightning sensor device driver

Required properties:
	- compatible: must be "ams,as3935"
	- reg: SPI chip select number for the device
	- spi-max-frequency: specifies maximum SPI clock frequency
	- spi-cpha: SPI Mode 1. Refer to spi/spi-bus.txt for generic SPI
	slave node bindings.
	- interrupt-parent : should be the phandle for the interrupt controller
	- interrupts : the sole interrupt generated by the device

	Refer to interrupt-controller/interrupts.txt for generic
	interrupt client node bindings.

Optional properties:
	- ams,tuning-capacitor-pf: Calibration tuning capacitor stepping
	  value 0 - 120pF. This will require using the calibration data from
	  the manufacturer.

Example:

as3935@0 {
	compatible = "ams,as3935";
	reg = <0>;
	spi-max-frequency = <400000>;
	spi-cpha;
	interrupt-parent = <&gpio1>;
	interrupts = <16 1>;
	ams,tuning-capacitor-pf = <80>;
};