hexagon: enable support for TOP_K op (#29113)
* hexagon: enable support for TOP_K op
* hex-topk: thread single-row TOP_K, raise VTCM-based size cap
* hex-topk: fix TOP_K mdev row partitioning
* hex-topk: optimize TOP_K large-row selection
* hexagon: clean up comment formatting
* hex-docs: update TOP_K support listings
