prepare new chan osc code

chan osc output will be 65536Hz - always
new functions for initializing the osc buffer and all

src/engine/platform/pcspkr.h

@@ -88,6 +88,7 @@ class DivPlatformPCSpeaker: public DivDispatch {
     void muteChannel(int ch, bool mute);
     bool keyOffAffectsArp(int ch);
     bool hasAcquireDirect();
+    bool isOscBufPositional();
     void setFlags(const DivConfig& flags);
     void notifyInsDeletion(void* ins);
     void notifyPlaybackStop();