Gowin: deal with active-low tristate (#2971)

* deal with active-low tristate

* remove empty port

* update sim models

* add expected lut1 to tests

techlibs/nexus/cells_map.v

@@ -58,7 +58,7 @@ module \$__NX_TINOUTPAD (input I, OE, output O, inout B);
 endmodule
 
 module \$__NX_TOUTPAD (input I, OE, output O);
-	OBZ _TECHMAP_REPLACE_ (.I(I), .O(), .T(~OE), .O(O));
+	OBZ _TECHMAP_REPLACE_ (.I(I), .T(~OE), .O(O));
 endmodule
 
 `ifndef NO_LUT