gitadora: (arena model) headphones i/o (#485)

## Link to GitHub Issue, if one exists
#477 

## Description of change
Plumb through headphone jack detection. Touch screen menu for headphone
volume lights up.

## Testing
Tested guitar.

src/spice2x/games/gitadora/io.h

@@ -11,6 +11,7 @@ namespace games::gitadora {
             Service,
             Test,
             Coin,
+            Headphone,
             GuitarP1Start,
             GuitarP1Up,
             GuitarP1Down,