[llvm] [AMDGPU][GlobalISel] Allow selecting buffer_load/store of pointers (PR #110714)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

And yep, I tried to do the `VTVec` thing (since SPIR-V has a `v2p64`) but then I started getting tablegen errors when trying to generate patterns for `v2p3` (there was some complaining about the type set being empty)

https://github.com/llvm/llvm-project/pull/110714