[M] Change in coreboot[main]: soc/intel/xeon_sp: Add PCIe root port driver

[Lean Sheng Tan (Code Review)]

Attention is currently required from: Arthur Heymans, Christian Walter, Cliff Huang, Jincheng Li, Johnny Lin, Jonathan Zhang, Lance Zhao, Patrick Rudolph, Shuo Liu, Tim Chu, Tim Wawrzynczak.

Lean Sheng Tan has posted comments on this change by Shuo Liu. ( https://review.coreboot.org/c/coreboot/+/81567?usp=email )

Change subject: soc/intel/xeon_sp: Add PCIe root port driver
......................................................................

Patch Set 12: Code-Review+2