[quant] Added reset_min_max_vals() function to observers (#60883)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60883
As per this [comment](https://github.com/pytorch/pytorch/pull/59964#discussion_r659064270), I created a `reset_min_max_vals()` function inside the observers which will be called during input-weight equalization. This is so that we will not expose the implementation of the observers in the equalization code.
Test Plan:
`python test/test_quantization.py TestEqualizeFx`
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D29491848
fbshipit-source-id: 00e91959ceb3b4f3688175a1a7ba11823e929b2f
