syslog: use nx_syslog in kernel space

[Kaben123]

Note: Please adhere to Contributing Guidelines.

Summary

This pull request introduces the use of nx_syslog in kernel space, providing a kernel-space equivalent to the standard syslog() function. The update ensures that system logging in the kernel is handled efficiently and consistently, while maintaining compatibility with user-space logging.

• Adds the nx_syslog function for kernel-space logging.
• Redefines syslog as nx_syslog when used in kernel space.
• Updates relevant headers and implementation files to support the new function.

Impact

• Enables consistent and efficient logging in kernel space using nx_syslog.
• No impact on user-space logging or existing syslog usage in user applications.
• Backward compatible for user-space code; kernel code now uses the new function transparently.

Testing

• Verified that kernel-space logging uses nx_syslog as expected.
• Confirmed that user-space logging remains unaffected.
• No regressions observed in system logging functionality.

[acassis]

@Kaben123 please follow the contribution guide, include the testing to prove it is working, etc. Seems like this commit never was tested, it is reporting primary errors like missing variables

[xiaoxiang781216]

@Kaben123 fix:

03160f973c syslog: use nx_syslog in kernel space
../nuttx/tools/checkpatch.sh -c -u -m -g dbbcd7c88ce1360e11773299657097fb39121c0a..HEAD
❌ Missing git commit message

[cederom]

Align to Contributing Guidelines.

[linguini1]

I believe this kind of change was already proposed by @wangchdo in #17018, and eventually the implementation in #17267 was merged . I don't see the added benefit of this change?