dt-bindings: i2c: add binding for Socionext SynQuacer I2C

Socionext SynQuacer I2C

Required properties:

- compatible      : Must be "socionext,synquacer-i2c"

- reg             : Offset and length of the register set for the device

- interrupts      : A single interrupt specifier

- #address-cells  : Must be <1>;

- #size-cells     : Must be <0>;

- clock-names     : Must contain "pclk".

- clocks          : Must contain an entry for each name in clock-names.

                    (See the common clock bindings.)

Optional properties:

- clock-frequency : Desired I2C bus clock frequency in Hz. As only Normal and

                    Fast modes are supported, possible values are 100000 and

                    400000.

Example :

    i2c@51210000 {

        compatible = "socionext,synquacer-i2c";

        reg = <0x51210000 0x1000>;

        interrupts = <GIC_SPI 165 IRQ_TYPE_LEVEL_HIGH>;

        #address-cells = <1>;

        #size-cells = <0>;

        clock-names = "pclk";

        clocks = <&clk_i2c>;

        clock-frequency = <400000>;

    };