DSP: Signal (faked) interrupt on every frame.

- Hack to work around games checking that the DSP event has been signaled by a real DSP interrupt.

src/core/hle/service/dsp_dsp.h

@@ -20,4 +20,7 @@ public:
     }
 };
 
+/// Signals that a DSP interrupt has occurred to userland code
+void SignalInterrupt();
+
 } // namespace