[llvm] [AMDGPU][MC] GFX9 - Support NV bit in FLAT instructions in pre-GFX90A (PR #154237)

[Stanislav Mekhanoshin via llvm-commits]

https://github.com/rampitec commented:

Also need negative MC tests where `nv` is unsupported.

https://github.com/llvm/llvm-project/pull/154237