Debug: Log number of GRFs at level sl=2 when loading a game

Add helper to get the number of non-static GRFs in a GRF config

src/sl/newgrf_sl.cpp

@@ -11,6 +11,7 @@
 #include "../fios.h"
 #include "../load_check.h"
 #include "../string_func.h"
+#include "../debug.h"
 
 #include "saveload.h"
 #include "newgrf_sl.h"
@@ -118,6 +119,7 @@ static void Load_NGRF_common(GRFConfig *&grfconfig)
 		if (IsSavegameVersionBefore(SLV_101)) c->SetSuitablePalette();
 		AppendToGRFConfigList(&grfconfig, c);
 	}
+	DEBUG(sl, 2, "Loaded %u NewGRFs", GetGRFConfigListNonStaticCount(grfconfig));
 }
 
 static void Load_NGRF()