[M] Change in coreboot[master]: soc: Remove useless extern prototypes in .h files

[Arthur Heymans (Code Review)]

Attention is currently required from: Christian Walter, Elyes Haouas, Fred Reitberger, Hung-Te Lin, Jakub Czapiga, Jason Glenesk, Jeff Daly, Johnny Lin, Julius Werner, Kapil Porwal, Matt DeVillier, Raul Rangel, Subrata Banik, Tarun Tuli, Tim Chu, Vanessa Eusebio, Yidi Lin, Yu-Ping Wu.

Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/76859?usp=email )

Change subject: soc: Remove useless extern prototypes in .h files
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Patch Set 1: Code-Review-2

(1 comment)

Patchset:

PS1: 
you should not declare variables inside headers. If you include the header in different places that will result in 2 separate variables with conflicting namespaces