Multiboard - F355 Challenge - route keyboard input to master

[benclau]

F355 games seems to work fine but since it needs 2 flycast instances (mutliboards), the controls are managed by the 1st instance and the graphics by the 2nd one. I/O instance only works when in focus and cannot work while the 2nd instance is in focus (e.g. fullscreen mode)

[flyinghead]

This is only an issue when using the keyboard, which isn't particularly useful for this game. Gamepads and other input controllers work without window focus.

[benclau]

It's working fine with a controller indeed. Thanks for the precision.