firmware: rework fritz-tools package

Split the fritz-tools into subpackages. fritz_tffs_read is usefull for
all Fritz boards where fritz-cal_extract is only required for the
Fritz 4040 at the moment.

Rename the tffs related binary to the more catchy name fritz_tffs and
move the whole package to utilities since the package doesn't really
provide a firmware file.

Make the fritz-tools available for all targets and build them shared.
The tffs is used by avm on lantiq and ar71xx as well.

Tested-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Mathias Kresin <dev@kresin.me>