[llvm] [AMDGPU][SIInsertWaitCnts] De-duplicate code (NFC) (PR #161161)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Looks like this is breaking the build with Clang:

```
../../../llvm/lib/Target/AMDGPU/SIInstrInfo.h:1036:15: error: class member cannot be redeclared
 1036 |   static bool isGFX12CacheInvOrWBInst(unsigned Opc) {
```

https://github.com/llvm/llvm-project/pull/161161