Intel fftw mpi update for MKL >= 11.1

I'm still wondering if there's a real need to include the name of the MPI library in the generated `cdft` library names... What's the benefit of this?

You can tell which MPI library was used when looking at the dependencies of this module. And I don't think using more than one MPI library at the same time when installing imkl makes sense.

So there will be only one version (of a particular precision) of the `libfftw_cdft` libraries anyway.

Not including a prefix would also avoid needing to update the dictionary if we happen to support an additional MPI library we're not supporting et.

Is there a downside to **not** including the MPI library name?