[Flang] Call the CSE pass in the pass pipeline

During the upstreaming process, it was decided to move contents
of the FIR CSE pass to the MLIR pass. Most of the FIR CSE changes
that are used are already moved to the MLIR pass. This patch calls
the MLIR CSE pass in places where the FIR CSE pass is called in the
pass pipeline.

Note: This is part of upstreaming from the fir-dev branch of
https://github.com/flang-compiler/f18-llvm-project.

Reviewed By: awarzynski, clementval

Differential Revision: https://reviews.llvm.org/D128365



Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>
Co-authored-by: Valentin Clement <clementval@gmail.com>
Co-authored-by: Andrzej Warzynski <andrzej.warzynski@arm.com>