Move a bunch more things into util package

A lot of utility code was just being imported willy-nilly from one
package to another. This moves the common code into util to make things
more sensible. The code moved were

 * The AsyncQueue and AsyncDecoupledCrossing from junctions.
 * All of the code in rocket's util.scala
 * The BlackBox asynchronous reset registers from uncore.tilelink2
 * The implicit definitions from uncore.util

src/main/scala/uncore/coherence/Policies.scala

@@ -5,7 +5,7 @@ package uncore.coherence
 import Chisel._
 import uncore.tilelink._
 import uncore.constants._
-import uncore.util._
+import util._
 
 /** The entire CoherencePolicy API consists of the following three traits:
   * HasCustomTileLinkMessageTypes, used to define custom messages