add serial build option for CMake

[rem1776]

Is your feature request related to a problem? Please describe.
The cmake build requires mpi currently, but we can build serially as well in our autotools build.

Describe the solution you'd like
Add an analogous serial option that removes the MPI dependency

Describe alternatives you've considered
n/a

Additional context
This is needed as part of our move towards cmake as the main supported build system.