[LTC] Upstream utils to extract BackendDevice from at::Tensor (#70069)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70069
This commit upstreams utils to extract BackendDevice from at::Tensor.
Test Plan: ./build/bin/test_lazy --gtest_filter=BackendDeviceTest.GetBackendDevice*
Reviewed By: wconstab
Differential Revision: D33172665
Pulled By: alanwaketan
fbshipit-source-id: b334ee358ea7b031bbffb0a16fa634715dba83f5
