netcf: support multilib builds

When doing a multilib build, /usr/lib is still created but not collected
into FILES_${PN} by default, resulting in a QA error.  Adding both
${libdir} and ${nonarch_libdir} catches all scenarios.

It also turns out that the previous do_install_append would throw an error
in a multilib build since systemd always installs to .../lib/... but
${libdir] would point at .../lib64/...

Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>