coolrunner2: Separate and improve buffer cell insertion pass

The new pass will contain all of the logic for inserting "passthrough"
product term and XOR cells as appropriate for the architecture. For
example, this commit fixes connecting an input pin directly to another
output pin with no logic in between.

techlibs/coolrunner2/synth_coolrunner2.cc

@@ -178,6 +178,7 @@ struct SynthCoolrunner2Pass : public ScriptPass
 			run("iopadmap -bits -inpad IBUF O:I -outpad IOBUFE I:IO -inoutpad IOBUFE O:IO -toutpad IOBUFE E:I:IO -tinoutpad IOBUFE E:O:I:IO");
 			run("attrmvcp -attr src -attr LOC t:IOBUFE n:*");
 			run("attrmvcp -attr src -attr LOC -driven t:IBUF n:*");
+			run("coolrunner2_fixup");
 			run("splitnets");
 			run("clean");
 		}