We now have the same API for MMIO and CPU registers.
Makes the code more concise, inntuitive, and improves readability.
https://crates.io/crates/register
In rust-lang/rust@679657b863 a breaking
change was introduced that now requires compiler_builtins. Add them,
and use the opportunity to kick out rlibc, since memset() et al. can
be provided by compiler intrinsics.