Add BF16 dtype mapping for python EVT

[gau-nernst]

Fixes #1824

I was thinking of adding a test case for this, but currently the dtype is hard-coded to FP16

https://github.com/NVIDIA/cutlass/blob/44dae8b90ef232ea663727470dfbbe9daff6972d/test/python/cutlass/evt/utils/evt_testbed.py#L206

Would take some refactoring to test multiple dtypes at the same time. Lmk if you want to add any tests, or don't add anything is fine.

@jackkosaian