[llvm] Perform bitreverse using AVX512 GFNI for i32 and i64. (PR #81764)

[via llvm-commits]

shamithoke wrote:

> Pull the GFNI setOperationAction calls out of the hasAVX512 case so any GFNI target can make use of it

I've put this check under hasAVX().

https://github.com/llvm/llvm-project/pull/81764