[mlir] make memref.subview produce strided layout

Memref subview operation has been initially designed to work on memrefs with
strided layouts only and has never supported anything else. Port it to use the
recently added StridedLayoutAttr instead of extracting the strided from
implicitly from affine maps.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D133938