Change in coreboot[master]: drivers/intel/fsp2_0: Allow `mp_startup_all_cpus()` to run serially

[Subrata Banik (Code Review)]

Attention is currently required from: Furquan Shaikh, Tim Wawrzynczak, Ravindra, Andrey Petrov, Patrick Rudolph.
Subrata Banik has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/57343 )

Change subject: drivers/intel/fsp2_0: Allow `mp_startup_all_cpus()` to run serially
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Patch Set 4:

(1 comment)

Patchset:

PS4: 
@Tim, please help to take a look in this CL, we need to pick this CL for sometime now to fix a regression and debug in on-going. if we could allow this to merge

Note: FSP has only one function that calls mp_startup_all_cpus for now in ADL and was not there in TGL so there is no chance for regression in previous generation. hence, we should be good once we have FSP fix in hand to revert.