[llvm] [AMDGPU] Move attributes to the bottom of a test file (NFC) (PR #219470)

[Jay Foad via llvm-commits]

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jayfoad wrote:

I much prefer putting the attributes inline:
```suggestion
define amdgpu_kernel void @test(ptr addrspace(1) %out, i32 %idx) "amdgpu-flat-work-group-size"="64,64" {
```

https://github.com/llvm/llvm-project/pull/219470