Change in coreboot[master]: soc/amd: move southbridge_smi_handler to common code

[Felix Held (Code Review)]

Attention is currently required from: Jason Glenesk, Raul Rangel.
Felix Held has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/50463 )

Change subject: soc/amd: move southbridge_smi_handler to common code
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Patch Set 4:

(1 comment)

Patchset:

PS4:
> I've always been cautious about moving SMIxnn register handling to common. […]

i verified stoneyridge, picasso and cezanne and even the older non-soc chips looked to be the same, so i'm confident enough to put it into the common code directory. i kept the defines in the soc-specific code, although the relevant ones are the same and the code has assumptions about some of the registers