[coreboot] PCIe Hotplug for Thunderbolt and U.2

[Jeremy Soller]

This is to continue the discussion from the coreboot leadership meeting. Thunderbolt devices are not correctly initialized by Coreboot such that the OS can boot without kernel parameters and allow for Thunderbolt hotplugging. Additional bus numbers and memory must be allocated.

I will be working on support for this for our System76 mainboards.

Here were the notes taken about it during the meeting, see 9 October 2019, PCIe Hotplug on newer Intel socs:

https://docs.google.com/document/d/1NRXqXcLBp5pFkHiJbrLdv3Spqh1Hu086HYkKrgKj...