[MLIR][LLVM] Add MemRead/MemWrite behavior to llvm store/load/addressof ops

This patch adds corresponding memory effects to mlir llvm-dialect load/store/addressof ops, which thus enables canonicalizations of those ops (like dead code elimination) that rely on the effect interface

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D117041