[llvm] [NVPTX] split long-running wmma.py test into smaller chunks. (PR #72331)

[Artem Belevich via llvm-commits]

Artem-B wrote:

This should help with https://github.com/llvm/llvm-project/issues/72285
It does not speed up the checks themselves, but splitting the tests should make them less of a bottleneck short-term.

https://github.com/llvm/llvm-project/pull/72331