[vulkan] Distribute weight prepacking along y dimension for conv2d (#48266)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/48266
Test Plan: Imported from OSS
Reviewed By: AshkanAliabadi
Differential Revision: D25222752
Pulled By: SS-JIA
fbshipit-source-id: 973e7956cd372c657dbbc6c7835e77b5f4e35f01
