spi: Add bindings for Lightning Mountain SoC

Lantiq Synchronous Serial Controller (SSC) SPI master driver

Required properties:

- compatible: "lantiq,ase-spi", "lantiq,falcon-spi", "lantiq,xrx100-spi"

- compatible: "lantiq,ase-spi", "lantiq,falcon-spi", "lantiq,xrx100-spi",

  "intel,lgm-spi"

- #address-cells: see spi-bus.txt

- #size-cells: see spi-bus.txt

- reg: address and length of the spi master registers

- interrupts: should contain the "spi_rx", "spi_tx" and "spi_err" interrupt.

- interrupts:

  For compatible "intel,lgm-ssc" - the common interrupt number for

  all of tx rx & err interrupts.

       or

  For rest of the compatibles, should contain the "spi_rx", "spi_tx" and

  "spi_err" interrupt.

Optional properties:

	num-cs = <6>;

	base-cs = <1>;

};

ssc0: spi@e0800000 {

	compatible = "intel,lgm-spi";

	reg = <0xe0800000 0x400>;

	interrupt-parent = <&ioapic1>;

	interrupts = <35 1>;

	#address-cells = <1>;

	#size-cells = <0>;

	clocks = <&cgu0 LGM_CLK_NGI>, <&cgu0 LGM_GCLK_SSC0>;

	clock-names = "freq", "gate";

};