ENH Adds label_smoothing to cross entropy loss (#63122)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/7455
Partially resolves pytorch/vision#4281
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63122
Reviewed By: iramazanli
Differential Revision: D30586076
Pulled By: jbschlosser
fbshipit-source-id: 06afc3aa1f8b9edb07fe9ed68c58968ad1926924
