Move nnapi code from ATen common code to specific library (#83748)
Summary: Currently we include nnapi code in all targets using ATen even if it's not used (actually there is no usage and being deprecated). Move it to `nnapi_backend_lib` for now.
Test Plan: Sandcastle.
Differential Revision: D38761095
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83748
Approved by: https://github.com/salilsdesai, https://github.com/SS-JIA
