NAMD: FIX build +cuda and mpi ~smp (#20778)
NAMD: FIX build +cuda and mpi ~smp (#20778)

* NAMD: FIX build +cuda

Hi,
If I try to compile NAMD with CUDA support, it fails because cannot file the file "{self.arch}.cuda" because it is undet the "arch" folder.

* NAMD: FIX mpi ~smp

Fix `spack install namd ^charmpp backend=mpi ~smp`
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack