YM2610(B): AY unification

as of now the SSG part of these chips is handled by a DivPlatformAY8910
within the DivPlatformYM2610.
this means less code duplication and therefore prepares for
OPN/OPNA support.

src/engine/platform/ay.cpp

@@ -493,6 +493,10 @@ int DivPlatformAY8910::getRegisterPoolSize() {
   return 16;
 }
 
+void DivPlatformAY8910::flushWrites() {
+  while (!writes.empty()) writes.pop();
+}
+
 void DivPlatformAY8910::reset() {
   while (!writes.empty()) writes.pop();
   ay->device_reset();