systemd: add packageconfig for wheel-group

If the distro does not include the group 'wheel' systemd will
complain when trying to parse ACL rules for tmpfiles.d.

  systemd-tmpfiles[273]: Failed to parse ACL "d:group:adm:r-x,d:group:wheel:r-x": Invalid argument. Ignoring

Systemd has a configuration parameter to avoid using 'wheel'
group in the standard config files for tmpfiles. Add this as
a PACKAGECONFIG and enable it by default to keep default.

Signed-off-by: Peter Bergin <peter@berginkonsult.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>