Reduce duplicates of channel struct

Add/Fix custom clock limit defines (for YMF278B)

src/engine/platform/fds.h

@@ -27,11 +27,11 @@
 #include "sound/nes_nsfplay/nes_fds.h"
 
 class DivPlatformFDS: public DivDispatch {
-  struct Channel {
-    int freq, baseFreq, pitch, pitch2, prevFreq, note, modFreq, ins;
+  struct Channel: public SharedChannelFreq, public SharedChannelVolume<signed char> {
+    int prevFreq, modFreq;
     unsigned char duty, sweep, modDepth, modPos;
-    bool active, insChanged, freqChanged, sweepChanged, keyOn, keyOff, inPorta, modOn;
-    signed char vol, outVol, wave;
+    bool sweepChanged, modOn;
+    signed short wave;
     signed char modTable[32];
     DivMacroInt std;
     void macroInit(DivInstrument* which) {
@@ -39,28 +39,16 @@ class DivPlatformFDS: public DivDispatch {
       pitch2=0;
     }
     Channel():
-      freq(0),
-      baseFreq(0),
-      pitch(0),
-      pitch2(0),
+      SharedChannelFreq(),
+      SharedChannelVolume<signed char>(32),
       prevFreq(65535),
-      note(0),
       modFreq(0),
-      ins(-1),
       duty(0),
       sweep(8),
       modDepth(0),
       modPos(0),
-      active(false),
-      insChanged(true),
-      freqChanged(false),
       sweepChanged(false),
-      keyOn(false),
-      keyOff(false),
-      inPorta(false),
       modOn(false),
-      vol(32),
-      outVol(32),
       wave(-1) {
       memset(modTable,0,32);
     }