Added an OpInfo for mm & ported its method_tests (#55446)
Summary:
Added an `OpInfo` for `mm` & ported its `method_tests` entry (it only had one).
cc: mruberry
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55446
Reviewed By: ngimel
Differential Revision: D27670883
Pulled By: mruberry
fbshipit-source-id: 51232f44ab01ad0454113992f80a4cfc730f8800
