I don't know if Tesla has any computers to license. My understanding is that nVidia makes the computers inside Tesla vehicles (the X1 product for infotainment, and the DRIVE product for self-driving).
I think John Deere is perfectly fine using something that is proven to work. I can't imagine anyone wanting to tie themselves to Tesla's software at this stage of the game.
https://blogs.nvidia.com/blog/2015/09/30/tesla-motors-model-...
https://www.nvidia.com/en-us/self-driving-cars/partners/tesl...
If you want to play with it, you can buy an X1/X2 devkit today, straight from nVidia : https://www.nvidia.com/en-us/autonomous-machines/embedded-sy...