[llvm] Update documentation for buffer fat pointers (PR #92034)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

@arsenm I meant this code right here https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AMDGPU/AMDGPUHSAMetadataStreamer.cpp#L120-L136 - it seems like if you provide type hints to your kernel, various buffer descriptors become "image" in the metadata?

https://github.com/llvm/llvm-project/pull/92034