[MLIR] Complete refactoring of Affine dialect into sub-libraries.

There were some unused CMakeFiles for Affine/IR and Affine/EDSC.
This change builds separate MLIRAffineOps and MLIRAffineEDSC libraries
using those CMakeFiles.  This combination replaces the old MLIRAffine
library.

Differential Revision: https://reviews.llvm.org/D78317