add channels last for GroupNorm (#49821)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49821
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D26007053
Pulled By: VitalyFedyunin
fbshipit-source-id: 34a48d5d3b66a159febf3c3d96748fbaba1b9e31
