GameCube 4-player Output

[RobertDaleSmith]

Currently the GameCube USBRetro output only supports single controller output. It may be possible to output all four players on a single RP2040 by adding 3 additional GPIO data lines for players 2, 3, and 4.

Some research needs to be done to evaluate whether the GC output lib used is small enough to run four simultaneous state machines on a single RP2040. If the PIOs instructions are small enough then it should fit no problem.

If so then a bit of refactoring will need to be done to handle this..

It should be able to detect whether one or more GC controller ports are connected. If more than one then split up USB input players to their reactive outputs. If only one then merge into copilot mode as it currently does.