Add missing x2son package (kicad stepup generated)
Another missing footprint as reported in https://github.com/KiCad/kicad-symbols/issues/520
This footprint is needed for the TPS3831 symbol. (Edit: merging this should fix both symbols missing a footprint in Power_Supervisor) Datasheet: http://www.ti.com/lit/ds/sbvs193d/sbvs193d.pdf
Generated using freecad and kicad stepup. The freecad file is included. I don't think we will need to split them out of the repo as of now. (If we get a lot of such contributions we might consider a footprint-source repo.)