Invalid CSR read for CSR=0x3b0 detected in BlackParrot cosimulation

[muwyse]

In BlackParrot testing with Dromajo cosimulation, at least one test reports out an invalid CSR read for the CSR with address 0x3b0 due to it being unimplemented in the processor.

Reproduce:
checkout black-parrot/black-parrot@111bac2 (dev branch)
cd bp_top/syn
make build.v sim.v CFG=e_bp_single_core_cfg SUITE=riscv_tests PROG=rv64ui-p-fence_i COSIM_P=1

[dpetrisko]

I think we discussed this offline, but for anyone curious: This is because we don't implement PMPs