popn: implement bi2x hook (#623)

## Link to GitHub Issue or related Pull Request, if one exists
#618 

## Description of change
Implement BI2X hook I/O for service/test/coin/headphones and the deka
pop-kuns.

src/spice2x/games/popn/io.h

@@ -11,6 +11,7 @@ namespace games::popn {
             Service,
             Test,
             CoinMech,
+            Headphone,
             Button1,
             Button2,
             Button3,
@@ -20,6 +21,8 @@ namespace games::popn {
             Button7,
             Button8,
             Button9,
+            RedPop,
+            BluePop
         };
     }