[quant][graphmode] Add quantization support for aten::dropout (#34347)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/34347
Test Plan:
python test/test_jit.py
Imported from OSS
Differential Revision: D20504453
fbshipit-source-id: 1bab29e21d0564ed88cdeb4894addfe00ebbd390
