torch.ao migration: fake_quantize.py, phase 1 (#64814)

torch.ao migration: fake_quantize.py, phase 1 (#64814)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64814

1. move the file
```
hg mv caffe2/torch/quantization/fake_quantize.py caffe2/torch/ao/quantization/
```

2. create a new file in the old location and copy the imports
3. fix all callsites inside `torch`

Test Plan:
```
buck test mode/dev //caffe2/test:quantization
```

Reviewed By: z-a-f

Differential Revision: D30866792

fbshipit-source-id: 7a221cb46c0ab01f1c5de9be061f09ecc83ce23e