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

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

> 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) {
> ```

Sorry for that, I landed a fix already: https://github.com/llvm/llvm-project/commit/da1eabd238d27c19ecc05580dff6361e5a0190d4

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