dbr quant: refactor first_call hooks to be standalone (#71324)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71324
In a future PR we need to start recording the DAG
of non-quantizeable ops, in order to properly reason about
function fusion.
This PR refactors the prepare hooks to have the first_call
versions be separate functions. This ensures that the logic
to record the DAG (the first_call functions) is separate
from the logic used at inference.
Test Plan:
```
python test/test_quantization.py -k DBR
```
Reviewed By: albanD
Differential Revision: D33588558
Pulled By: vkuzo
fbshipit-source-id: 7b27ee4e5b64f26bfb082ca2bbf2c04894bd2a97
(cherry picked from commit 21fa63566976e0d369e6d9f97453b4e82833d4a6)
