tilelink: Xbar now allows for fanout control

src/main/scala/diplomacy/Parameters.scala

@@ -293,3 +293,14 @@ object BufferParams
   val flow    = BufferParams(1, true, false)
   val pipe    = BufferParams(1, false, true)
 }
+
+case class TriStateValue(value: Boolean, set: Boolean)
+{
+  def update(orig: Boolean) = if (set) value else orig
+}
+
+object TriStateValue
+{
+  implicit def apply(value: Boolean): TriStateValue = TriStateValue(value, true)
+  def unset = TriStateValue(false, false)
+}