[Quant][fx] Decouple prepare_*fx from training/eval modes (#75401)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75401
This commit removes asserts that require prepare_fx to
be run in eval mode and prepare_qat_fx to be run in training mode.
Test Plan:
python test/test_quantization.py TestQuantizeFx.test_prepare_mode
Imported from OSS
Reviewed By: vkuzo, jerryzh168
Differential Revision: D35457100
fbshipit-source-id: 13a55b13d9e389991f69c06c6a70bc51cdebba36
(cherry picked from commit fb0685e0873dc8e807da3213be403b51e8b4a687)
