fix mimpid

Created by: davideschiavone

Fix mimpid

According to https://docs.openhwgroup.org/projects/cv32e40p-user-manual/en/latest/core_versions.html#cv32e40p-v2-0-0, we need to set the mimpid to 1 when the parameters related to custom and floating-point ISA extensions are set to inform the users that the core is not logically equivalent to the frozen version v1.0.0.