Cpuio features out-of-date

[NightEule5]

The cpuio crate doesn't build on the latest nightly since due to features being removed. const_fn has been stable for a while now, and llvm_asm was deprecated in 1.56 in favor of asm, which itself was stabilized in 1.59. Any nightly version >1.60 with not build this crate. Both features could be removed and the crate can build on stable now.