Switch Int8Softmax, Int8Relu, and Int8LeakyRelu to QNNPACK (#14933)
Summary:
Int8Softmax: 4x-5x speedup compared to previous implementation
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14933
Differential Revision: D13406820
Pulled By: Maratyszcza
fbshipit-source-id: ea8cbe1b861ddb7ff1b851d06d52c6fd6d04ed01
