[llvm] [AMDGPU][NFC] Add divergent tests for amdgcn.exp2, amdgcn.sqrt and rsq (PR #196527)

[Jay Foad via llvm-commits]

jayfoad wrote:

I don't think these belong in `pseudo-scalar-transcendental.ll‎`. It was specifically for testing support for the pseudo scalar transcendental instructions. General tests like this would normally go in e.g. `test/CodeGen/AMDGPU/llvm.amdgcn.exp2.ll` -- are we missing some test cases there?

https://github.com/llvm/llvm-project/pull/196527