[llvm] [NVPTX] Improve folding to mad with immediate 1 (PR #93628)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B commented:

`mul(m, n+1) -> mad(m,n,m)` makes sense.

`mul(m, select(1, n)) -> select(mul(m,n), m)` -- not so much. Perhaps I'm missing something.

https://github.com/llvm/llvm-project/pull/93628