[mlir][linalg] Fix vectorization of linalg depthwise conv for int types

Vectorization of Linalg's depthwise convolution only supports floating
point types. Previous version assumed floating point operations would
work. This version checks whether the computation is integer or floating
point and adjust the inner loop computation.

Reviewed By: hanchung

Differential Revision: https://reviews.llvm.org/D137595