Merge pull request #2356 from whitequark/flatten-techmap-no-tpl_driven-sigmap

flatten, techmap: don't canonicalize tpl driven bits via sigmap

tests/techmap/bug2183.ys

@@ -0,0 +1,11 @@
+read_verilog <<EOT
+module foo(inout a, b);
+  assign a = b;
+endmodule
+module bar(output c);
+  foo f(c, 1'b0);
+endmodule
+EOT
+
+hierarchy -auto-top
+flatten