[FS] Add GetFreeBytes

include/services/fs.hpp

@@ -43,6 +43,7 @@ class FSService {
 	void controlArchive(u32 messagePointer);
 	void deleteFile(u32 messagePointer);
 	void formatSaveData(u32 messagePointer);
+	void getFreeBytes(u32 messagePointer);
 	void getFormatInfo(u32 messagePointer);
 	void getPriority(u32 messagePointer);
 	void initialize(u32 messagePointer);