added FP for AS3956-ATDx

Created by: cyber-murmel

for https://github.com/KiCad/kicad-symbols/pull/1636

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 footprint(s) you are contributing
  • https://ams.com/documents/20143/36005/AS3956_DS000546_7-00.pdf#page=95
• An example screenshot image is very helpful
  • 
• If there are matching symbol or 3D model pull requests, provide link(s) as appropriate
• Check the output of the Travis automated check scripts - fix any errors as required
• Give a reason behind any intentional library convention rule violation.