Updates smmla unrolling patterns to handle vecmat contracts where `dimM=1`. This includes explicit vecmats in the form: `<1x8xi8> x <8x8xi8> --> <1x8xi32>` or implied with the leading dim folded: `<8xi8> x <8x8xi8> --> <8xi32>`
Since the smmla operates on two `<2x8xi8>` input vectors to produce `<2x2xi8>` accumulators, half of each 2x2 accumulator tile is dummy data not pertinent to the computation, resulting in half throughput.
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