fake_quant: move observer and fake_quant flags into buffers (#38368)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38368
There is a need for some customers to enable/disable these flags
in the middle of QAT. To make it work properly with DDP,
we need to implement them using buffers so that they are replicated
properly to all the nodes.
This should solve issue https://github.com/pytorch/pytorch/issues/38081
Test Plan:
CI
Imported from OSS
Differential Revision: D21537607
fbshipit-source-id: 8c9da022beb7aaa44c658268f02f99dd5aee93fd
