[mlir][linalg] Add NHWC + FHWC Img2Col (#68708)

Adds the Img2Col transformation for the fhwc channel ordering in a
Conv2D. Because of how the channel ordering affects the matrix
dimensions in the flattened filter this results in a slightly different
implementation of the actual "matrix multiplication". Instead of doing a
regular row-column dot-product this arrangement requires a row-row dot
product, otherwise the filter matrix would first need to be transposed.

Adds a lit test to the transform dialect to check the semantics of the
optimization are correct.

Signed-off-by: Jack Frankland <jack.frankland@arm.com>