Add aten::flatten NNAPI converter (#60885)
Summary:
Add support for aten::div op in the NNAPI model converter. Startup time
variable size support isn't supported as shapes go as inputs to NNAPI op
Runtime variable size support to supported soon
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60885
Test Plan: pytest test/test_nnapi.py::TestNNAPI::test_flatten
Reviewed By: anshuljain1
Differential Revision: D29451725
fbshipit-source-id: 8902745f7758c8cc88ad4b4ce02b8301ff894bd4
