[XLA:GPU] Move SoftMax output tile size calculation to TritonFusion.
[XLA:GPU] Move SoftMax output tile size calculation to TritonFusion.

We have the same logic that finds reduce in a SoftMax fusion duplicated to calculate tile sizes and launch dimensions. It's better to have everything in TritonFusion, so we can also get tile sizes in Cost Model.

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/12975 from Intel-tensorflow:kanvi/fix_mm_tests 6ff6bd59a20fdabaf450134d6b449348a7a3c2ed
