[M] Change in coreboot[main]: soc/intel/xeon_sp: Add get_cxl_mode

[Lean Sheng Tan (Code Review)]

Attention is currently required from: Angel Pons, Arthur Heymans, Christian Walter, Jincheng Li, Johnny Lin, Jonathan Zhang, Patrick Rudolph, Shuo Liu, Tim Chu.

Lean Sheng Tan has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/82092?usp=email )

Change subject: soc/intel/xeon_sp: Add get_cxl_mode
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Patch Set 9: Code-Review+2