Change PoolOp Functors design to support CuDNN CUDA fallback (#15903)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15903
Change PoolOp Functors design to support CuDNN CUDA fallback
Reviewed By: houseroad
Differential Revision: D13617085
fbshipit-source-id: 8a539d77f35bc47afe5dc8e32aaad52e45cb691c
