Reland "[MLIR][LLVM] Change addressof builders to use opaque pointers" (#69292)

This relands fbde19a6, which was broken due to incorrect GEP element type creation.

This commit changes the builders of the `llvm.mlir.addressof` operations
to no longer produce typed pointers.

As a consequence, a GPU to NVVM pattern had to be updated, that still
relied on typed pointers.