GitLab

* [Feature] Add revert_sync_batchnorm

* support mmsyncbn (to be tested)

* Test passed

* Update docstring, rename the test file

* remove test_sync_bn

* add comment

* add mmcv.ops check

* Add a comment

* Add notes and relax test req
Co-authored-by: gaotongxiao <gaotongxiao@gmail.con>