[llvm] [NVPTX] Fix and refine prefetch.* intrinsics (PR #126899)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B approved this pull request.

LGTM

Note: normally removing/changing public-facing APIs like intrinsics requires extra steps to avoid breaking existing users, or a fairly long deprecation sequence.

However in this case the original changes we're refining here were made only a day ago in #125887, so we're OK without autoupgrading the old intrinsics. 



https://github.com/llvm/llvm-project/pull/126899