[NNC] fix Half conversion of immediates in Cuda backend (#45213)
Summary:
The Cuda HalfChecker casts up all loads and stores of Half to Float, so we do math in Float on the device. It didn't cast up HalfImmediate (ie. constants) so they could insert mixed-size ops. Fix is to do that.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45213
Reviewed By: ezyang
Differential Revision: D23885287
Pulled By: nickgg
fbshipit-source-id: 912991d85cc06ebb282625cfa5080d7525c8eba9
