[XS] Change in coreboot[main]: soc/intel/elkhartlake: Hook up S0ix setting to option API

[Jérémy Compostella (Code Review)]

Attention is currently required from: Intel coreboot Reviewers, Matt DeVillier, Werner Zeh.

Jérémy Compostella has posted comments on this change by Matt DeVillier. ( https://review.coreboot.org/c/coreboot/+/87499?usp=email )

Change subject: soc/intel/elkhartlake: Hook up S0ix setting to option API
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Patch Set 2: Code-Review+1