Added SA612A mixer

Replace this line with your commit message! Please provide a description of your pull request

---

All contributions to the kicad library must follow the KiCad library convention

Thanks for creating a pull request to contribute to the KiCad libraries! To speed up integration of your PR, please check the following items:

• Provide a URL to a datasheet for the symbol(s) you are contributing

• An example screenshot image is very helpful

• Ensure that the associated footprints match the official footprint library

  • A new fitting footprint must be submitted if the library does not yet contain one.

• If there are matching footprint PRs, provide link(s) as appropriate

• Check the output of the automated check scripts - fix any errors as required

• Give a reason behind any intentional library convention rule violation.