[llvm] [AMDGPU] Avoid repeated parsing in generic classification test (PR #225551)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

test/TableGen should not be including any real target definition files. The entire point of these tests is to test and debug tablegen itself, without the heavyweight baggage of the real uses 

https://github.com/llvm/llvm-project/pull/225551