SIMD version average pooling added (#22148)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22148
Average pooling is added into dnnlowp optimization code.
Reviewed By: jspark1105
Differential Revision: D15936556
fbshipit-source-id: 6177ee62529801898f230c6fb89e9c4b598593a5
