Binding for Silicon Labs 544 programmable I2C clock generator.

Reference
This binding uses the common clock binding[1]. Details about the device can be
found in the datasheet[2].

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
[2] Si544 datasheet
    https://www.silabs.com/documents/public/data-sheets/si544-datasheet.pdf

Required properties:
 - compatible: One of "silabs,si514a", "silabs,si514b" "silabs,si514c" according
               to the speed grade of the chip.
 - reg: I2C device address.
 - #clock-cells: From common clock bindings: Shall be 0.

Optional properties:
 - clock-output-names: From common clock bindings. Recommended to be "si544".

Example:
	si544: clock-controller@55 {
		reg = <0x55>;
		#clock-cells = <0>;
		compatible = "silabs,si544b";
	};