Fix broken windows build due per channel quantization stack land. (#38828)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38828
Move newly introduced functions in qnnpack_utils.h inside the ifdef.
Test Plan: CI.
Reviewed By: malfet
Differential Revision: D21672942
fbshipit-source-id: 32e23bb45f5f3f882618e91435a1ae9f80781f97
