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#6731Closes#7809