[L] Change in coreboot[main]: soc/intel/xeon_sp: Unshare Xeon-SP chip common codes

[Nico Huber (Code Review)]

Attention is currently required from: Arthur Heymans, Christian Walter, David Hendricks, Johnny Lin, Jonathan Zhang, Lean Sheng Tan, Martin L Roth, Patrick Rudolph, Paul Menzel, Shuo Liu, TangYiwei, Tim Chu.

Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81312?usp=email )

Change subject: soc/intel/xeon_sp: Unshare Xeon-SP chip common codes
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Patch Set 23:

(1 comment)

File src/soc/intel/xeon_sp/chip_gen1.c:

https://review.coreboot.org/c/coreboot/+/81312/comment/6881b0ae_5e4c3e03 :
PS16, Line 192: #if CONFIG(SOC_INTEL_HAS_CXL)
> Updated. I keep the create_cxl_domain as non-static, thus it could cover all cases.

There are plenty of options, you could also do this:
```
void create_cxl_domains(const union xeon_domain_path dp, struct bus *bus,
                        const STACK_RES *sr, const size_t pci_segment_group);
#if CONFIG(SOC_INTEL_HAS_CXL)
void create_cxl_domains(const union xeon_domain_path dp, struct bus *bus,
                        const STACK_RES *sr, const size_t pci_segment_group)
{
        ...
```
Or you could put the declaration into a local header file.

IMO, polluting the public API space is not a good solution.