Change in coreboot[master]: lib/thread: Add mutex

[Furquan Shaikh (Code Review)]

Attention is currently required from: Raul Rangel, Eric Peers, Felix Held.
Furquan Shaikh has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/56230 )

Change subject: lib/thread: Add mutex
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Patch Set 7:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/56230/comment/bdc743e9_532947dc 
PS7, Line 14: 
            : If a task (A) wishes to yield control to the next task (B) that is
            : holding onto the mutex, without encountering a delay of its own
            : (i.e., udelay(0)), then we need to ensure the next task (B) is at the
            : head of the queue. We do this by using a `0 us` delay in mutex_lock. If
            : we were to use anything larger than a `0 us` delay, a `udelay(0)` by the
            : task (A) that just unlocked the mutex will most likely not schedule the
            : next task (B) that was holding onto the mutex.
Maybe its just me. But I find this example really confusing. The logic in the code makes sense, but this explanation confused me :P.