Change in coreboot[master]: intel/common/../systemagent: Add sa_get_mchbar_base api

[Wonkyu Kim (Code Review)]

Attention is currently required from: Subrata Banik, Tim Wawrzynczak, Paul Menzel, Angel Pons, Arthur Heymans, Michael Niewöhner.
Wonkyu Kim has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/63615 )

Change subject: intel/common/../systemagent: Add sa_get_mchbar_base api
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Patch Set 16:

(1 comment)

Patchset:

PS16:
> > @Subrata, I'm not worried about #2 because if one forgets to enable MCHBAR early the resulting iss […]

@Subrata and @Angel,

Can we summarize solution?
1. Remove init part in case of MCBAR is not enabled in sa_get_mchbar_base API?
or
2. use MCH_BASE_ADDRESS in ioc.c

And enable in soc bootblock

For #2, it's already implemented before but we updated while we adding this logic.
https://review.coreboot.org/c/coreboot/+/63198/12/src/soc/intel/common/block...