REALHBF16 binary ops: maximum, minimum, mul (#6009)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/6009

- mul:              1.69 M -> 15 K
- maximum:    353 K -> 11 K
- minimum:     353 K -> 11 K
ghstack-source-id: 246985131
exported-using-ghexport

Reviewed By: swolchok

Differential Revision: D63909726

fbshipit-source-id: 83b87bd789026194f65067ea952c57b83266583f