[mlir] Move memref.subview patterns to MemRef/Transforms/

These patterns have been used as a prerequisite step for lowering
to SPIR-V. But they don't involve SPIR-V dialect ops; they are
pure memref/vector op transformations. Given now we have a dedicated
MemRef dialect, moving them to Memref/Transforms/, which is a more
suitable place to host them, to allow used by others.

This commit just moves code around and renames patterns/passes
accordingly. CMakeLists.txt for existing MemRef libraries are
also improved along the way.

Reviewed By: mravishankar

Differential Revision: https://reviews.llvm.org/D100326