[mlir] simplify affine maps and operands in affine.min/max

Affine dialect already has a map+operand simplification infrastructure in
place. Plug the recently added affine.min/max operations into this
infrastructure and add a simple test. More complex behavior of the simplifier
is already tested by other ops.

Addresses https://bugs.llvm.org/show_bug.cgi?id=45008.

Differential Revision: https://reviews.llvm.org/D75058