Put everything in the same workspace

[tomaka]

Cargo is currently experimenting with fixing long-standing issues with dependencies being pulled when they shouldn't:
rust-lang/cargo#7915
rust-lang/cargo#7914

Once this is stable enough, we should simply put everything in the same workspace in order to simplify the build process.

[tomaka]

I just remembered that this was not possible because Cargo will put a lock in the workspace during the building. When the kernel is being built, it will try to build the modules as part of the build, which will then lock forever.