Get rid of global constructors in cuda codegen (#40183)
Summary:
Use switch instead of look ups in global std::unordered_maps<> to do enum-to-name conversions.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40183
Reviewed By: malfet
Differential Revision: D22117731
Pulled By: ionsphere
fbshipit-source-id: d150114cfae5b1222bb9142d815f2379072506c7
