[mlir][Linalg] Fix and improve vectorization of depthwise convolutions.

When trying to connect the vectorization of depthwise convolutions to e2e execution
a number of problems surfaced.
Fix an off-by-one error on the size of the input vector (similary to what was previously done for regular conv).
Rewrite the lowering to vector.fma instead of vector.contract: the KW reduction dimension has already been unrolled and vector.contract requires a reduction dimension to be valid.

Differential Revision: https://reviews.llvm.org/D113884