posix: convert all error logs to debug logs

In Zephyr, things are often optimized for size first. That's how
we fit into such tight parking spaces.

This change gives more control to the user about whether the
POSIX API does any logging at all, simultaneously shrinking binary
size while improving speed.

No bytes / cycles left behind!

Signed-off-by: Christopher Friedt <cfriedt@meta.com>