Remove the use of macros in defining binary ops for base Vec256 (#33733)
Summary:
This greatly improves readability and maintainability (e.g., debugging)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33733
Differential Revision: D20103187
Pulled By: ezyang
fbshipit-source-id: e539e46f5d378a2b01da7ecaa6b850655e0fa866
