[llvm] [NVPTX] Legalize aext-load to zext-load to expose more DAG combines (PR #154251)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

We also see some JAX test failures that bisect here, specifically testSort and testSortAgainstNumpy: https://github.com/jax-ml/jax/blob/3d52f5f87095189c3c619fb9daff3259a519aaad/tests/lax_test.py#L2528. I don't have any repro instructions or public buildbots to point to however.

https://github.com/llvm/llvm-project/pull/154251