Use Makefile.crates instead of Makefile's CARGO_CRATES

From: Nuno Teixeira <eduardo_at_freebsd.org>
Date: Fri, 23 Sep 2022 19:49:57 UTC
Hello to all!

I've just created a PR that sugests using Makefile.crates so we can have
nicer, cleaner Makefiles in Rust/cargo ports.

Any opinions are welcome!

*Bug 266571* <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=266571>

Thanks,
-- 
Nuno Teixeira
FreeBSD Committer (ports)