MMC3: Make sure to free any allocated memory when using MMC3 as an external module.

src/boards/mmc3.h

@@ -21,6 +21,7 @@ extern void (*mwrap)(uint8 V);
 void GenMMC3Power(void);
 void GenMMC3Restore(int version);
 void MMC3RegReset(void);
+void GenMMC3Close(void);
 void FixMMC3PRG(int V);
 void FixMMC3CHR(int V);
 DECLFW(MMC3_CMDWrite);