add BFloat16 support for AdaptiveAvgPool2d on CPU (#56902)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/56902
Test Plan: Imported from OSS
Reviewed By: mikaylagawarecki
Differential Revision: D28836789
Pulled By: VitalyFedyunin
fbshipit-source-id: caac5e5b15190b8010bbfbc6920aa44032208ee7
