os: Implement os::Mutex

[Nitr4m12]

This is mostly based on DWARF info and work I have done on nn::atk. There really doesn't seem to be more to these functions other than just calling the global Mutex functions.

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This change is 

[german77]

@german77 reviewed 1 file and all commit messages.
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[Pistonight]

I would probably also get rid of the todo comment otherwise LGTM

[MonsterDruide1]

@MonsterDruide1 reviewed 1 file and all commit messages, and made 2 comments.
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include/nn/os/os_Mutex.h line 9 at r1 (raw file):

// todo: figure out where these go
void InitializeMutex(MutexType*, bool recursive, s32 lockLevel);

Suggestion:

void InitializeMutex(MutexType*, bool recursive, s32 lockLevel);

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include/nn/os/os_Mutex.h line 51 at r1 (raw file):

};

}  // namespace nn::os

add newline at end of file

Suggestion:

}  // namespace nn::os

[MonsterDruide1]

@MonsterDruide1 reviewed 1 file and all commit messages, and resolved 2 discussions.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on Nitr4m12).