[llvm] [AMDGPU] Move kernarg preload logic to AMDGPU Attributor (PR #123547)

[Austin Kerbow via llvm-commits]

kerbowa wrote:

> Why do we want to move it to this file? I'm not sure if this is the good place. I think this file is only for things that run part of the attributor framework.

It needs to be part of a module pass since it does things like cloning and deleting functions. I had a PR up to make AMDGPULowerKernelArguments a module pass, but I think the consensus was that it made sense to unify all the inreg/preload kernarg functionality here.

https://github.com/llvm/llvm-project/pull/123547