TensorIterator norm update (#31903)
Summary:
special case for norm out where p == 2. Instead of calling `pow`,
we use multiplication as a faster code path.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31903
Differential Revision: D19312749
Pulled By: ngimel
fbshipit-source-id: 73732b7b37a243a14438609784795b920271a0b5
