Optimize GroupNorm on CPU (#28203)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28203
Optimize GroupNorm on CPU
ghstack-source-id: 105149765
Test Plan: buck test mode/dev-nosan caffe2/test:nn -- "GroupNorm"
Reviewed By: houseroad
Differential Revision: D17901506
fbshipit-source-id: 5eb22ad0e8a9ab2533282b967b2818f690e48865
