Change in coreboot[master]: lib: Add a mutex

[Kyösti Mälkki (Code Review)]

Attention is currently required from: Raul Rangel, Nico Huber, Tim Wawrzynczak, Angel Pons, Julius Werner, Rob Barnes, Karthik Ramasubramanian.
Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59320 )

Change subject: lib: Add a mutex
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Patch Set 15:

(1 comment)

Patchset:

PS15: 
Well I am generally against direct replacement of spinlock with mutex like suggested in your followup work, so I cannot really give this a positive review score. Does not prevent others from doing that.

There are CB:60253 and CB:60280 available as alternative approach to solve COOP_MULTITASKING deadlock.