Services/NIM: Implement CheckForSysUpdateEvent.

Implementation verified by reverse engineering.
This lets the Home Menu boot without crashing on startup.

src/core/hle/service/nim/nim.h

@@ -10,6 +10,17 @@ class Interface;
 
 namespace NIM {
 
+/**
+ * NIM::CheckForSysUpdateEvent service function
+ *  Inputs:
+ *      1 : None
+ *  Outputs:
+ *      1 : Result of function, 0 on success, otherwise error code
+ *      2 : Copy handle descriptor
+ *      3 : System Update event handle
+ */
+void CheckForSysUpdateEvent(Service::Interface* self);
+
 /**
  * NIM::CheckSysUpdateAvailable service function
  *  Inputs: