[Quant][fx] Hide equalization_config from prepare APIs (#80164)
Summary: This PR hides the equalization_config argument from
prepare_fx. This is a private API that we do not wish to expose
to users and have to maintain backward compatibility for.
Test Plan:
python test/test_quantization.py TestEqualizeFx
Reviewers: jerryzh168
Subscribers: jerryzh168
Differential Revision: [D37394353](https://our.internmc.facebook.com/intern/diff/D37394353)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80164
Approved by: https://github.com/jerryzh168
