Don't register firmware already in /var/db/pkg

Don't register firmware already in /var/db/pkg

If installing firmware with `make install` from a port, it doesn't register
properly by adding "@option firmware" to the packing list, this means we ignore
that it is installed and reinstall it over and over with the registration
ending up in a tmpdir named directory inside the existing directory in
/var/db/pkg.

Unfortunately I don't know of a good way to automatically clean up from that,
so we just print a message after installing the actual firmware.

Reported by job@
No complaints about the patch on tech@ for several weeks.