* Liebherr's BK4 controller external SPI

A device which handles data acquisition from compatible industrial
peripherals.
The SPI is used for data and management purposes in both master and
slave modes.

Required properties:

- compatible : Should be "lwn,bk4"

Required SPI properties:

- reg : Should be address of the device chip select within
  the controller.

- spi-max-frequency : Maximum SPI clocking speed of device in Hz, should be
  30MHz at most for the Liebherr's BK4 external bus.

Example:

spidev0: spi@0 {
	compatible = "lwn,bk4";
	spi-max-frequency = <30000000>;
	reg = <0>;
};
