[llvm] [LLVM] Make use of s_flbit_i32_b64 and s_ff1_i32_b64 (PR #75158)

[Acim Maravic via llvm-commits]

Acim-Maravic wrote:

> LGTM with test tweaks.
> 
> Should also do GlobalISel as Matt mentioned, but that can be a separate patch.

I updated the tests.

I will do GlobalISel in another patch.

https://github.com/llvm/llvm-project/pull/75158