Refactor package hierarchy and remove legacy bus protocol implementations (#845)

* Refactors package hierarchy.

Additionally:
  - Removes legacy ground tests and configs
  - Removes legacy bus protocol implementations
  - Removes NTiles
  - Adds devices package
  - Adds more functions to util package

src/main/scala/rocket/PMP.scala

@@ -1,12 +1,12 @@
 // See LICENSE.SiFive for license details.
 
-package rocket
+package freechips.rocketchip.rocket
 
 import Chisel._
 import Chisel.ImplicitConversions._
-import config._
-import tile._
-import util._
+import freechips.rocketchip.config._
+import freechips.rocketchip.tile._
+import freechips.rocketchip.util._
 
 class PMPConfig extends Bundle {
   val l = Bool()