linux-firmware: Compress firmware on disk

linux-firmware: Compress firmware on disk

This patch enabled that we can compress any firmware files on disk. This
will save some space since /lib/firmware is becoming larger with every
release.

From formerly 828MiB, this is now using ~349MiB which is a saving of
about 480MiB on disk. This is helping us a lot fighting to contain the
distribution to 2GB on /.

Some other firmware that is installed in other packages is not
compressed with this patch which is a bit sad, but potentially not worth
the effort.

In order to ship this change with a Core Update, it might be intuitive
to remove /lib/firmware first and then extract the new update with all
new files. However, I do not know if this all will compress as well as
before since now the files are already individually compressed. It might
be a challenge to ship this.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>