spi: Add DT bindings for Synquacer

This patch adds documentation for Device-Tree bindings for the
Socionext Synquacer spi driver.

Signed-off-by: Masahisa Kojima <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/spi/spi-synquacer.txt

···
+* 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;
+	};