Add the seastar-cpu-map.sh to the SBINFILES variable, which is used to create symbolic links to scripts so that they appear in $PATH. Please note that there are additional Python scripts (like perftune.py), which are not in $PATH. That's because Python scripts are handled separately in "install.sh" and no Python script has a "sbin" symlink. We might want to change this in the future, though. Fixes #6731 Closes #7809