Add threadpool in qlinear and qconv for mobile (#26728)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26728
Use Caffe2::mobile_threadpool() in linear and conv operators
Perf
Without threadpool - 76ms
With threadpool - 41 ms
Test Plan:
python test/test_quantized.py TestQNNPackOps
Imported from OSS
Differential Revision: D17553510
fbshipit-source-id: dd5b06f526f65d87727ec7e3dad0a5fa74cba9f9
