fbcode_builder: getdeps: fboss: add OpenBCM fetcher
fbcode_builder: getdeps: fboss: add OpenBCM fetcher

Summary: As titled

Differential Revision: D18726457

fbshipit-source-id: 717a6cda4a78e1b246f20328df1f01b78560cac5

facebook/wangle,facebook/wangle,facebook/wangle