Split button board into 2 16 button joysticks.

WPILib was unhappy with more than 16 buttons.

Change-Id: I3b874678d262245912f0f67896d8db6562fd8742
diff --git a/aos/common/input/driver_station_data.h b/aos/common/input/driver_station_data.h
index 507ad61..874b90c 100644
--- a/aos/common/input/driver_station_data.h
+++ b/aos/common/input/driver_station_data.h
@@ -41,7 +41,7 @@
       : JoystickFeature(joystick, number) {}
 
   // How many buttons there are available on each joystick.
-  static const int kButtons = 12;
+  static const int kButtons = 16;
 };
 
 // Represents the direction of a POV on a joystick.