Implement ql_syscall_sched_yield

[vhertz]

Checklist

Which kind of PR do you create?

• This PR only contains minor fixes.
• This PR contains major feature update.
• This PR introduces a new function/api for Qiling Framework.

Coding convention?

• The new code conforms to Qiling Framework naming convention.
• The imports are arranged properly.
• Essential comments are added.
• The reference of the new code is pointed out.

Extra tests?

• No extra tests are needed for this PR.
• I have added enough tests for this PR.
• Tests will be added after some discussion and review.

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Target branch?

• The target branch is dev branch.

One last thing

• I have read the contribution guide

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I implemented ql_syscall_sched_yield() for POSIX's sched_yield(2). It stops the emulation of a current thread and sets _sched_yield() to its sched_cb.

Should I write a new test for this?

[wtdcode]

LGTM

[xwings]

If you have a binary and src for this will be awesome.

I will merge for now and and test can be in later.