[llvm] MCExpr-ify amd_kernel_code_t (PR #91587)

[Janek van Oirschot via llvm-commits]

JanekvO wrote:

Also removing `AMDKernelCodeTUtils.h/.cpp` files. Was expecting to use some calls within `AMDGPUMCKernelCodeT.h/.cpp` but I didn't so better suited to remove. Might even be better to replace code in `AMDKernelCodeTUtils` to `AMDGPUMCKernelCodeT` and remove `AMDGPUMCKernelCodeT` instead. Do let me know what everybody thinks.

https://github.com/llvm/llvm-project/pull/91587