This adds a simple rewrite/legalization to decompose constant splats larger than a single ArmSME tile into multiple SME virtual tile sized splats. E.g. a constant splat to `vector<[8]x[8]xi32>` would decompose into four `vector<[4]x[4]xi32>` splats.
This adds a simple rewrite/legalization to decompose constant splats larger than a single ArmSME tile into multiple SME virtual tile sized splats. E.g. a constant splat to `vector<[8]x[8]xi32>` would decompose into four `vector<[4]x[4]xi32>` splats.