make: separate installation and de-duplication targets

make: separate installation and de-duplication targets

For better or worse some distributions cannot have the firmware
de-duplication happen automatically.

In addition, when it was introduced it changed the default behaviour
leaving people with no firmware in their systems.

Revert to the original behaviour: in the worst case, people will have a
few MB extra of duplicate firmware, yet their systems will continue to
work.

To make things stand out, we print a message at the end of install so
that everyone can opt-in as needed.

In addition, I've went ahead and opened tentative MR/PR with Alpine,
Arch, CentOS Stream, Debian, Gentoo, informing them of this change.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>