[llvm] Reapply "[AMDGPU][GlobalISel] Fix load/store of pointer vectors, buffer.*.pN (#110714)" (PR #111059)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

Note: I have no idea why https://lab.llvm.org/buildbot/#/builders/63/builds/1865 would've filed and this is very much a "works on my machine" situation. Does anyone have any theories?

https://github.com/llvm/llvm-project/pull/111059