Binding for Silicon Labs 514 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] Si514 datasheet
    https://www.silabs.com/Support%20Documents/TechnicalDocs/si514.pdf

Required properties:
 - compatible: Shall be "silabs,si514"
 - 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 "si514".

Example:
 si514: clock-generator@55 {
  reg = <0x55>;
  #clock-cells = <0>;
  compatible = "silabs,si514";
 };