Accessing pmpcfg1 on RV64 is not an illegal instruction

[kkapapu]

Describe the bug

csrr a0, pmpcfg1

NutShell treats pmpcfg1 as a legal CSR and commits the instruction.

Expected behavior

RISC-V Privileged Spec CSR table: pmpcfg1 and pmpcfg3 are RV32 only. On RV64, access must raise illegal-instruction.

Expected: mcause=2, mtval=0x3a102573
Actual: mcause=0, the CSR read commits
CSR.scala still contains MaskedRegMap(Pmpcfg1, pmpcfg1) (and Pmpcfg3).

Environment

NutShell: 041f694