Add debug option to disable FMA usage.

[jjsjann123]

🚀 Feature

Our end-2-end testing always compare the output of fuser with Pytorch eager. Since PyTorch eager execute binary operation one after the other, versus fuser which does multiple operation as a whole. FMA used in fuser kernel provides better accuracy, but it drifts away from the eager result.

We would want a quick flag to disable FMA usage just to avoid such numerical issue in functional test.

Assigning myself on this.