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/groundtest/Package.scala

@@ -1,5 +1,9 @@
 // See LICENSE.SiFive for license details.
 
+package freechips.rocketchip
+
 package object groundtest {
   val testRamAddr = 0x10000
+  val timeoutCodeBits = 4
+  val errorCodeBits = 4
 }