add channels last for AdaptiveAvgPool2d (#48916)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48916
optimize adaptive average pool2d forward path
optimize adaptive average pool2d backward path
remove unused headers
minor change
minor change
rename the header; add adaptive max pooling in future.
minor change
loosen adapative_pool2d test on nhwc to both device cuda and cpu
minor change
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D25399469
Pulled By: VitalyFedyunin
fbshipit-source-id: 86f9fda35194f21144bd4667b778c861c05a5bac
