Update:

> OCuLink won't be available in single-CPU configuration.

Apparently, OCuLink won‘t be available at all:

"μPCIe connector [...] is incorrectly identified as OCuLink [...] due to errors that were discovered post-production in IBM OpenPOWER reference designs. While the physical connector is the same as OCuLink ports, the wiring is different, notably in the presence detect / clocking pins. As such, while an OCuLink peripheral is unlikely to be damaged by being plugged in to the μPCIe port, it will not function while attached."
https://wiki.raptorcs.com/w/images/e/e3/T2P9D01_users_guide_version_1_0.pdf (page 69)