[Kernel] Implement GetHeadphoneStatus, stub SignalEvent

include/kernel/kernel.hpp

@@ -114,6 +114,7 @@ class Kernel {
 	void getThreadID();
 	void releaseMutex();
 	void sendSyncRequest();
+	void signalEvent();
 	void svcCloseHandle();
 	void connectToPort();
 	void outputDebugString();

include/services/dsp.hpp

@@ -50,6 +50,7 @@ class DSPService {
 
 	// Service functions
 	void convertProcessAddressFromDspDram(u32 messagePointer); // Nice function name
+	void getHeadphoneStatus(u32 messagePointer);
 	void getSemaphoreHandle(u32 messagePointer);
 	void loadComponent(u32 messagePointer);
 	void readPipeIfPossible(u32 messagePointer);