[Asooka]

Yes, those customizations are made by AMD. They aren't even very custom, fail0verflow have managed to run a lightly modified linux kernel with the open-source AMD drivers on PS4 hardware with full graphics acceleration[0].

[0] https://fail0verflow.com/blog/2016/console-hacking-2016-post...

[catdog]

As far as I know this are more or less custom configurations of the same CPU i.e. how many CPU/GPU cores, how much cache etc.