[llvm] [AMDGPU] Move kernarg preload logic to separate pass (PR #130434)

[Austin Kerbow via llvm-commits]

kerbowa wrote:

If anyone has opinions about the best approach for this please let me know because we need to do something. There are three PRs up that are achieving the same end, but I don't want to just rebase/update all three. At different points I've seen interest in each approach based on discussion in the PRs.

1. #130434
2. #123547
3. #112790

@arsenm @shiltian @krzysz00 

https://github.com/llvm/llvm-project/pull/130434