Let bfloat16 support promotion with other types (#41698)
Summary:
Fix https://github.com/pytorch/pytorch/issues/40580
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41698
Reviewed By: albanD
Differential Revision: D22824042
Pulled By: mruberry
fbshipit-source-id: 7dad9c12dc51d8f88c3ca963ae9c5f8aa2f72277
