[llvm] AMDGPU: Migrate Analysis/Transforms tests to amdgpu subarch triple (2) (PR #208810)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I noticed some of these now just use `amdgpu` as the the architecture component. Which architecture is `amdgpu`?

None, it's the dummy target. When all of this migration is done, it will be an error to codegen it. It still works fine for random analyses and pure transform tests

https://github.com/llvm/llvm-project/pull/208810