First cut at refactoring unittests into a top-level utility. Individual tests co-located with their DUT. No functional changes.

src/main/scala/groundtest/Generator.scala

@@ -6,6 +6,7 @@ import uncore.devices.NTiles
 import uncore.constants._
 import junctions._
 import rocket._
+import util.Timer
 import scala.util.Random
 import cde.{Parameters, Field}