The "RISC-V State Enable Extension" was ratified at the end of at the
end of last year though hasn't yet been integrated in the main
specification documents (see
https://wiki.riscv.org/display/TECH/Recently+Ratified+Extensions).
This commit adds the CSRs defined by this extension in
https://github.com/riscv/riscv-state-enable/releases/download/v0.6.3/Smstateen.pdf.
Note I've defined the CSRs together in a single foreach loop. This is easiest to read when compared to the Smstateen spec. If/when these CSRs are merged into the tables in the privileged spec, we may want to loop back to match however they are grouped there.
Is mstateen here twice?