[llvm] [NVPTX] Use prmt.f4e to lower pointer alignment fshr idiom (PR #143407)

[Justin Fargnoli via llvm-commits]

https://github.com/justinfargnoli approved this pull request.

Ignorable nit: could be nice to test the other cases (0, 1, 2) and add negative test cases. 

LGTM regardless :)  

https://github.com/llvm/llvm-project/pull/143407