[quant][be] Easier way to override default in QConfigMapping (#99888)
Summary: This commit adds a private helper function to override
the default QConfig in the default QConfigMapping. Previously we
needed to override all the object_types manually while skipping
the fixed qparams ops. This led to duplicate code every time
someone wanted a new default QConfig. After this commit, we can
just call the same helper function instead.
Test Plan:
python test/test_quantization.py TestQuantizeFx
Reviewers: jerryzh168, vkuzo
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99888
Approved by: https://github.com/vkuzo, https://github.com/jerryzh168
