mcounteren CSR should not exist

Created by: Silabs-ArjanB

The official RISC-V spec was updated in response to https://github.com/riscv/riscv-isa-manual/issues/561, see https://github.com/riscv/riscv-isa-manual/commit/1eaebccc78d88f110a68faf1b39938fc291a4065 and comments on that commit).

We should remove mcounteren from CV32E40P (this issue relates to #432 (closed) as well, but the related questions have not been answered yet in the RISC-V organization).