[llvm] [AMDGPU] Add amdgpu-lower-exec-sync pass to lower named-barrier globals (PR #165692)

[via llvm-commits]

skc7 wrote:

> > I don't see the changes that remove the logic from LowerModuleLDS? Are they missing?
> > EDIT: Ah I see, they're in the next PR that enables the pass. Please update the PR description to reflect that
> 
> I don't really see why we need three separate commits for this. It's just existing code getting rebundled into a pass, and that pass is being enabled by default in its new intended place. All this _should_ be done as a single change. This kind of split can hide complexity and errors. With a single change, if anything breaks, then either things were not as simple as they seem, or errors were introduced. But it will all be trackable to this one change.

For any pass that will be newly introduced in the amdgpu backend, developers usually follow the approach of two PRs
1. Creating the pass, with both legacy and new pass manager implementations.
2. Adding the pass into the `amdgpu` pipeline.

Have followed the same for this change as well. Additionally, removal of changes from `lower-module-lds` were made into separate PR as per feedback from @shiltian 

https://github.com/llvm/llvm-project/pull/165692