allow external backend codegen to toggle whether to generate out= and inplace kernels (#68530)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/68530
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D32498569
Pulled By: bdhirsh
fbshipit-source-id: ebd932d042b988e19c71aa04a21677db9bdc9f04
