[llvm] [AMDGPU][RFC] Combine asm and disasm tests. (PR #90214)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I hope that we do not add new MCStreamer derivatives just for testing purposes.
For round tripping tests, can you do `llvm-mc ... -filetype=obj | llvm-objdump -d -` instead?

https://github.com/llvm/llvm-project/pull/90214