Add option to preserve certain methods during optimize_for_mobile. (#40629)
Summary:
By default freeze_module pass, invoked from optimize_for_mobile,
preserves only forward method. There is an option to specify a list of
methods that can be preserved during freeze_module. This PR exposes that
to optimize_for_module pass.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40629
Test Plan: python test/test_mobile_optimizer.py
Reviewed By: dreiss
Differential Revision: D22260972
Pulled By: kimishpatel
fbshipit-source-id: 452c653269da8bb865acfb58da2d28c23c66e326
