[L] Change in coreboot[main]: doc/arch/x86: Add MP-Init documentation

[Patrick Rudolph (Code Review)]

Attention is currently required from: Angel Pons, Benjamin Doron, Felix Held, Felix Singer, Martin Roth, Maximilian Brune, Nicholas Chin.

Patrick Rudolph has posted comments on this change by Maximilian Brune. ( https://review.coreboot.org/c/coreboot/+/86772?usp=email )

Change subject: doc/arch/x86: Add MP-Init documentation
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Patch Set 7:

(5 comments)

File Documentation/arch/x86/mp_init.md:

https://review.coreboot.org/c/coreboot/+/86772/comment/d0f1fe2f_f1d3f551?usp... :
PS7, Line 41: mp_cpu_bus_init
What's `mp_cpu_bus_init`? It was never defined, never explained and is never used outside of the title.

https://review.coreboot.org/c/coreboot/+/86772/comment/3db31715_14ec8c96?usp... :
PS7, Line 61: usually
The interresting case is when it's unusual. When is it not using `ap_init()` and why?

https://review.coreboot.org/c/coreboot/+/86772/comment/716b2a09_f7cc8d03?usp... :
PS7, Line 94: fancy
what's fancy about it? How's it done on other systems?

File Documentation/arch/x86/mp_init.svg:

https://review.coreboot.org/c/coreboot/+/86772/comment/aa124381_e03366d8?usp... :
PS7, Line 1: <?
I'd prefer a UML sequence diagramm. This diagramm is missing syncronization points, which is important in concurrent systems.

File Documentation/arch/x86/mp_init_entry.svg:

https://review.coreboot.org/c/coreboot/+/86772/comment/ce5a5e32_faf58756?usp... :
PS7, Line 1: <?
Unclear when which path is taken