spi: Add DT bindings for Synquacer

* Socionext Synquacer HS-SPI bindings

Required Properties:

- compatible: should be "socionext,synquacer-spi"

- reg: physical base address of the controller and length of memory mapped

       region.

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

- clocks: core clock iHCLK. Optional rate clock iPCLK (default is iHCLK)

- clock-names: Shall be "iHCLK" and "iPCLK" respectively

Optional Properties:

- socionext,use-rtm: boolean, if required to use "retimed clock" for RX

- socionext,set-aces: boolean, if same active clock edges field to be set.

Example:

	spi0: spi@ff110000 {

		compatible = "socionext,synquacer-spi";

		reg = <0xff110000 0x1000>;

		interrupts = <GIC_SPI 160 IRQ_TYPE_LEVEL_HIGH>,

			     <GIC_SPI 161 IRQ_TYPE_LEVEL_HIGH>,

			     <GIC_SPI 162 IRQ_TYPE_LEVEL_HIGH>;

		clocks = <&clk_hsspi>;

		clock-names = "iHCLK";

		socionext,use-rtm;

		socionext,set-aces;

	};