Update multi-chip API for harnesses

generators/firechip/src/main/scala/FireSim.scala

@@ -77,6 +77,8 @@ class FireSim(implicit val p: Parameters) extends RawModule with HasHarnessInsta
   def referenceReset = resetBridge.io.reset
   def success = { require(false, "success should not be used in Firesim"); false.B }
 
+  override val supportsMultiChip = true
+
   instantiateChipTops()
 
   // Ensures FireSim-synthesized assertions and instrumentation is disabled