[mlir][Affine] Introduce affine memory interfaces

This patch introduces interfaces for read and write ops with affine
restrictions. I used `read`/`write` intead of `load`/`store` for the
interfaces so that they can also be implemented by dma ops.
For now, they are only implemented by affine.load, affine.store,
affine.vector_load and affine.vector_store.

For testing purposes, this patch also migrates affine loop fusion and
required analysis to use the new interfaces. No other changes are made
beyond that.

Co-authored-by: Alex Zinenko <zinenko@google.com>

Reviewed By: bondhugula, ftynse

Differential Revision: https://reviews.llvm.org/D79829