* Energy Micro EFM32 SPI

Required properties:
- #address-cells: see spi-bus.txt
- #size-cells: see spi-bus.txt
- compatible: should be "energymicro,efm32-spi"
- reg: Offset and length of the register set for the controller
- interrupts: pair specifying rx and tx irq
- clocks: phandle to the spi clock
- cs-gpios: see spi-bus.txt
- efm32,location: Value to write to the ROUTE register's LOCATION bitfield to configure the pinmux for the device, see datasheet for values.

Example:

spi1: spi@0x4000c400 { /* USART1 */
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "energymicro,efm32-spi";
	reg = <0x4000c400 0x400>;
	interrupts = <15 16>;
	clocks = <&cmu 20>;
	cs-gpios = <&gpio 51 1>; // D3
	efm32,location = <1>;
	status = "ok";

	ks8851@0 {
		compatible = "ks8851";
		spi-max-frequency = <6000000>;
		reg = <0>;
		interrupt-parent = <&boardfpga>;
		interrupts = <4>;
		status = "ok";
	};
};