[llvm] [AMDGPU] Move WWM register pre-allocation to during regalloc (PR #70618)

[Matt Arsenault via llvm-commits]

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

Really the allocator should be handling this, so as we move towards that point it makes sense to move where this runs 

https://github.com/llvm/llvm-project/pull/70618