Cardreader read/write open methods

Marlin/src/sd/cardreader.h

@@ -83,7 +83,8 @@ public:
   static void checkautostart();
 
   // Basic file ops
-  static void openFile(char * const path, const bool read, const bool subcall=false);
+  static void openFileRead(char * const path, const uint8_t subcall=0);
+  static void openFileWrite(char * const path);
   static void closefile(const bool store_location=false);
   static void removeFile(const char * const name);