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

[Raul Rangel (Code Review)]

Attention is currently required from: Julius Werner, Kyösti Mälkki, Rob Barnes, Karthik Ramasubramanian.
Raul Rangel 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 9:

(2 comments)

File src/lib/mutex.c:

https://review.coreboot.org/c/coreboot/+/59320/comment/72286616_a96f339c 
PS8, Line 12: 			return;
> They don't belong in spinlock.h since the mutex and spinlock use different algorithms. […]

Done

https://review.coreboot.org/c/coreboot/+/59320/comment/18a983f8_1f08945d 
PS8, Line 27: 		} while (__atomic_load_1(&mutex->locked, __ATOMIC_RELAXED));
> static __always_inline int spin_is_locked(x) […]

Done