Add new CSRs defined in Privileged Spec version 1.12 (#90)
Add new CSRs defined in Privileged Spec version 1.12 (#90)

* Add CSRs defined in Privileged spec 1.12 (non-H)

This commit defines additional CSRs defined in the privileged
specification, version 1.12 (diff is from 1.11) except...

-   Those defined in riscv-opcodes:
    -   mstatush
    -   mtinst
    -   mtval2
    -   mcontext
-   Those related to hypervisor extension

cf. <https://github.com/riscv/riscv-isa-manual/releases/tag/Priv-v1.12>

* Add new CSRs defined in Privileged spec 1.12 (H)

New hypervisor-related CSRs, `henvcfg` and `henvcfgh` are added.
All other hypervisor-related CSRs are already implemented in
riscv-opcodes.

cf. <https://github.com/riscv/riscv-isa-manual/releases/tag/Priv-v1.12>
riscv/riscv-opcodes,riscv/riscv-opcodes