[csrng/rtl] Discuss whether we should remove the `INVALID_GEN_CMD` status error response

### Description

Currently there there is a command status error response code called `INVALID_GEN_CMD` for the case where the ctr_drbg generate stage answers to a command that is not a generate command. This should theoretically only happen in the case of a fault injection.
We need to discuss if this cmd status error response is still worth having or if we want to remove it as we did for the uninstantiate zeroize check.