add mising VSX dispatches (#51217)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/51132
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51217
Reviewed By: malfet
Differential Revision: D26120485
Pulled By: ezyang
fbshipit-source-id: d83384964f9980c9a921d0c7159f07e88025ea92
