dbr quant: do not crash on unsupported qconfig_dict keys if they are empty (#71233)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71233
Some keys in qconfig_dict are not implemented yet for DBR quant.
However, FX graph mode quantization modifies qconfig_dict inplace,
so if users use the same dict for DBR and FX they may hit errors.
This PR reduces the chance of these errors by only throwing an
exception in DBR quant if the unsupported keys have nonempty values.
Test Plan:
```
python test/test_quantization.py TestQuantizeDBR.test_qconfig_dict_unsupported_only_crashes_when_nonempty
```
Reviewed By: samdow
Differential Revision: D33552398
Pulled By: vkuzo
fbshipit-source-id: 4191ad7ae23929455fef6acaf2c045c65db0b0bd
(cherry picked from commit 8b1911f33e1298225055aff375c0479760767468)
