Add FakeQuantize Module (#21767)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21767
Adding FakeQuantize Module
for quantization aware training
Reviewed By: dzhulgakov
Differential Revision: D15728503
fbshipit-source-id: 2a9a6a362812ede3deac42b93dddca35987bd8e6
