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

[NAKAMURA Takumi via llvm-commits]

chapuni wrote:

Looks like this has triggered failures again; https://lab.llvm.org/buildbot/#/builders/63/builds/1905
(and my private builders)

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