[vulkan] enable prepacking for Batchnorm op (#88433)
Adds a `BatchNormPackedContext` so that the `batchnorm` op can use prepacking.
Differential Revision: [D40721546](https://our.internmc.facebook.com/intern/diff/D40721546/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88433
Approved by: https://github.com/manuelcandales
