[mlir][LLVM] Enable opaque-pointers in e2e lowering test pass

Part of https://discourse.llvm.org/t/rfc-switching-the-llvm-dialect-and-dialect-lowerings-to-opaque-pointers/68179

Given this is only a test pass I believe it should be fine to switch it to opaque-pointers entirely while migrating.

Differential Revision: https://reviews.llvm.org/D144726