C64: finish it all

all modules play correctly, bar:
- motherfunksignal (almost)
- filters are a bit weird

src/engine/platform/sms.h

@@ -34,6 +34,7 @@ class DivPlatformSMS: public DivDispatch {
     void acquire(short* bufL, short* bufR, size_t start, size_t len);
     int dispatch(DivCommand c);
     void tick();
+    bool keyOffAffectsArp();
     int init(DivEngine* parent, int channels, int sugRate);
 };