[XLA:GPU] Move Tiling Complexity heuristic to EmitMatMul.
[XLA:GPU] Move Tiling Complexity heuristic to EmitMatMul.

Currently the heuristic lives in the wrong place. It requires to pass fusion_kind to TritonWrapper.

The heuristic is used only for GEMMs, so it should move either up (to TritonFusion::Emit), or down (to EmitMatMul). I chose EmitMatMul because it requires less changes to the current infrastructure.
