[mlir][GPU] Add op for unrolling contractions to a native size

Adds `apply_patterns.gpu.unroll_vectors_subgroup_mma` which allows
specifying a native MMA shape of `m`, `n`, and `k` to unroll to,
greedily unrolling the inner most dimension of contractions and other
vector operations based on expected usage.

Differential Revision: https://reviews.llvm.org/D156079