PIO statemachines for i/o handoff

[borb]

At present, the keyboard and mouse aspects rely entirely on CPU-centric operation. core0 runs the keyboard events and USB stack. During a keyboard event, no USB events are handled at all which could cause latency, and the next USB event is only handled once the keycode is completely sent.

Similarly, though not as intensive as the keycode transmission, mouse events are handled entirely on a loop by core1.

Replacing both of these by independant PIO handlers will offload the CPU aspect and leave the CPU free to handle USB events, possibly decreasing the as-yet-unmeasured latency.