[llvm] [AMDGPU] - Add constant folding for s_bitreplicate (PR #72366)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I implemented the `s_bitreplicate` constant folding, as mentioned in [#69209 (comment)](https://github.com/llvm/llvm-project/pull/69209#discussion_r1374324260).
> 
> However, I don't think I can do the same for the `s_wqm` and `s_quadmask` intrinsics, because they implicitly set SCC?

But the intrinsics don't expose the SCC output so it doesn't matter. Nearly every SCC def is useless 

https://github.com/llvm/llvm-project/pull/72366