This reverts commit a84a961a39.
The changes to RegisterCrossing.scala were unneeded after application of this branch.
The name changes made to the AsyncQueue.scala are reapplied at the end of this branch.
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