iopadmap: Add native support for negative-polarity output enable.

techlibs/xilinx/cells_map.v

@@ -359,11 +359,3 @@ module \$__XILINX_MUXF78 (O, I0, I1, I2, I3, S0, S1);
   else
     MUXF8 mux8 (.I0(T0), .I1(T1), .S(S1), .O(O));
 endmodule
-
-module \$__XILINX_TINOUTPAD (input I, OE, output O, inout IO);
-  IOBUF _TECHMAP_REPLACE_ (.I(I), .O(O), .T(~OE), .IO(IO));
-endmodule
-
-module \$__XILINX_TOUTPAD (input I, OE, output O);
-  OBUFT _TECHMAP_REPLACE_ (.I(I), .O(O), .T(~OE));
-endmodule