Temporarily use HTIF to push RTC value to cores

uncore/src/main/scala/uncore.scala

@@ -6,6 +6,7 @@ import Chisel._
 case object NReleaseTransactors extends Field[Int]
 case object NProbeTransactors extends Field[Int]
 case object NAcquireTransactors extends Field[Int]
+case object RTCPeriod extends Field[Int]
 
 trait CoherenceAgentParameters extends UsesParameters {
   val nReleaseTransactors = 1