fastio.h: Add AT90USBxx_TEENSYPP_ASSIGNMENTS for teensyduino/Lincomatic/...

fastio.h: Add AT90USBxx_TEENSYPP_ASSIGNMENTS for teensyduino/Lincomatic/Printrboard compatibility.

This could close issue https://github.com/ErikZalm/Marlin/issues/703 https://github.com/ErikZalm/Marlin/issues/112 and https://github.com/ErikZalm/Marlin/pull/708