[llvm] [AMDGPU] Form V_MAD_U64_U32 from mul24 (PR #72393)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

@jayfoad, can you answer the speed model questions? I don't know enough about it to answer those. Thanks

https://github.com/llvm/llvm-project/pull/72393