Implement ArReadFSDualWord() routine

sdk/xtdk/i686/arfuncs.h

@@ -57,6 +57,10 @@ XTCDECL
 ULONG_PTR
 ArReadControlRegister(IN USHORT ControlRegister);
 
+XTCDECL
+ULONG
+ArReadFSDualWord(ULONG Offset);
+
 XTCDECL
 ULONGLONG
 ArReadModelSpecificRegister(IN ULONG Register);