Dear Michal:
Thank you very much!
I found it at page 845 (21.1.36, 21.1.37) of the Intel 300 PCH Datasheet Vol. 2 that you gently provided.
I got the configurations from the lspci.log / xHCI Host Controller offsets 0xB0h and 0xD0h and I set them into my devicetree.
Have a nice day, Jose Trujillo.