arch-riscv: Implement rv32 zicsr extension

1. Add misc register mstatush, cycleh, timeh, instreth,
   hpmcounter03...hpmcounter31, pmpcfg1, pmpcfg3
2. Implement handling RV32 only registers
3. Implement methods of set time CSR

Change-Id: I5c55c18a0da91977d6e23da24ea3cbcba9f0509b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65733
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
5 files changed