[stage] Make config concatenation actually work

generators/chipyard/src/main/scala/stage/ChipyardAnnotations.scala

@@ -11,7 +11,12 @@ private[stage] object UnderscoreDelimitedConfigsAnnotation extends HasShellOptio
   override val options = Seq(
     new ShellOption[String](
       longOption = "legacy-configs",
-      toAnnotationSeq = a => Seq(new ConfigsAnnotation(a.split("_"))),
+      toAnnotationSeq = a => {
+        val split = a.split('.')
+        val packageName = split.init.mkString(".")
+        val configs     = split.last.split("_")
+        Seq(new ConfigsAnnotation(configs map { config => s"${packageName}.${config}" } ))
+      },
       helpText = "A string of underscore-delimited configs (configs have decreasing precendence from left to right).",
       shortOption = Some("LC")
     )