Add missing packages

[iamashwin99]

Few packages that are already there in spack and require minimal effort include :

• [x] nfft
• [x] pnfft
• [x] berkeleygw
• [ ] sparskit
• [x] etsf-io

[fangohr]

For etsf-io, we can perhaps continue https://github.com/fangohr/octopus-in-spack/pull/13 ?

[iamashwin99]

I had a look at #13, i felt that it would be easier to add the 3 lines than to deal with the merge conflict that comes when rebasing with that MR.

[fangohr]

Just close #13 when you have extract the relevant information and used it elsewhere.