register-rs 1.0.0 now uses UnsafeCell internally, which means we lost the Copy
derive on InMemoryRegister.
Therefore, a small set of changes was needed in the MMU driver to dance around
the static array init depending on a Copy type.
`rustup target add aarch64-unknown-none-softfloat` is now a thing.
It is no longer required to build rust-std on-demand with `xbuild`.
This reduces compile-times significantly.