Initial AMD EPYC Genoa Support Added To Coreboot, New Onyx Motherboard Target

Going along with AMD's work on AMD openSIL for open-sourcing the CPU silicon initialization code to ultimately replace AGESA in future hardware platforms, the initial EPYC "Genoa" code for Coreboot has been upstreamed along with the Onyx motherboard target.

AMD openSIL initially supports EPYC 9004 "Genoa" processors and the initial motherboard supported by it happens to be their Onyx reference motherboard. So it's interesting to see the AMD Onyx reference motherboard also being the first Genoa board supported by Coreboot and not their more common Titanite 2P reference design.

This commit added the initial "minimal viable code for compilation" of the AMD Genoa SoC target. Following that was also adding the minimal implementation of the AMD Onyx motherboard.

This is just the start of the AMD 4th Gen EPYC "Genoa" enablement for Coreboot with this work being done both by AMD engineers and the 9elements security consulting firm. There is also a lot more Genoa code under review for Coreboot.