z80pack: Move devfd somewhere common

Begin folding all the common z80pack bits together
z80pack: devfd updates
z80pack-lite: clean up config, use common devfd
z80pack-lite: bring up to date a bit more
z80pack-lite: clean up old code
z80pack-lite: bring into alignment with modernity
micropack: use the shared devfd
z80pack-lite: get it to build again

Not yet tested
z80pack-lite: link _discard suitably
Merge remote-tracking branch 'origin/master' into zx128-clean