Add support for Softmax. (#45286)
Summary:
This PR adds support for Softmax in NNC.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45286
Reviewed By: mrshenli
Differential Revision: D24042901
Pulled By: navahgar
fbshipit-source-id: 120bafe17586d3ecf0918f9aee852a7c3a8f4990
