Fixed naming issues in packages

* new scheme: chisel.axi is the main package
* chisel.axi.Axi4 contains the full axi defs
* chisel.axi.Axi4Lite contains the lite defs
* chisel.axi.axi4 contains full Axi4 impls
* chisel.axi.axi4lite contains lite impls
* same applies for the generators, matching structure

src/main/scala/AxiModuleBuilder.scala

 package chisel.axiutils
-import  chisel.axiutils.axi4lite._, chisel.axiutils.axi4._
+import  chisel.axi.axi4lite._, chisel.axi.axi4._
 import  chisel.packaging._, chisel.packaging.CoreDefinition.root
 import  chisel.miscutils.DecoupledDataSource, chisel.miscutils.Logging
 import  scala.sys.process._

src/main/scala/axi4/AxiFifoAdapter.scala

-package chisel.axiutils
+package chisel.axi.axi4
 import  chisel.axi._
 import  chisel.miscutils.Logging
 import  chisel3._

src/main/scala/axi4/FifoAxiAdapter.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel.axi._
 import  chisel.miscutils._
 import  chisel3._

src/main/scala/axi4/Mux.scala

-package chisel.axiutils
+package chisel.axi.axi4
 import  chisel3._
 import  chisel3.util._
 import  chisel.axi.Axi4._

src/main/scala/axi4/SlidingWindow.scala

-package chisel.axiutils
+package chisel.axi.axi4
 import  chisel.miscutils.{DataWidthConverter, Logging}
 import  chisel.axi._
 import  chisel3._

src/main/scala/axi4lite/RegisterFile.scala

-package chisel.axiutils.axi4lite
+package chisel.axi.axi4lite
 import  chisel.axi._, chisel.axi.Axi4Lite
 import  chisel.miscutils.Logging
 import  chisel3._

src/main/scala/axi4lite/Registers.scala

-package chisel.axiutils.axi4lite
+package chisel.axi.axi4lite
 import  Chisel.{Reg, UInt}
 
 /**

src/main/scala/axi4lite/package.scala

-package chisel.axiutils
+package chisel.axi
+
 package object axi4lite {
   /** Tuple-type for bit ranges. */
   sealed case class BitRange(to: Int, from: Int) {

src/test/scala/axi4/Axi2AxiSuite.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel.axi.Axi4._
 import  chisel3._
 import  chisel3.util._

src/test/scala/axi4/AxiMuxSuite.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel.axi.Axi4._
 import  chisel.axiutils._
 import  chisel.miscutils.Logging

src/test/scala/axi4/SlaveModel.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel3._, chisel3.util._
 import  chisel3.iotesters.{PeekPokeTester}
 import  chisel.axi._

src/test/scala/axi4/SlidingWindowSuite.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel.axi.Axi4._
 import  chisel.axi._
 import  chisel.axiutils._

src/test/scala/axi4/package.scala

-package chisel.axiutils.axi4
+package chisel.axi.axi4
 import  chisel.axi._
 import  chisel.axi.Axi4._
 import  chisel.miscutils.generators._

src/test/scala/axi4lite/ProgrammableMaster.scala

-package chisel.axiutils.axi4lite
+package chisel.axi.axi4lite
 import  chisel3._
 import  chisel3.util._
 import  chisel.axi._

src/test/scala/axi4lite/RegisterFileSpec.scala

-package chisel.axiutils.axi4lite
+package chisel.axi.axi4lite
 import  chisel.axi._
 import  chisel.axi.Axi4Lite, chisel.axi.Axi4Lite._
 import  chisel.axi.generators.Axi4Lite._

src/test/scala/axi/generators.scala → src/test/scala/generators.scala

 package chisel.axi
-import  chisel.axi.generators._
 import  chisel.miscutils.generators._
 import  org.scalacheck.{Arbitrary, Gen}
 
@@ -28,7 +27,7 @@ package object generators {
 
   object Axi4Lite {
     import chisel.axi.Axi4Lite._
-    import chisel.axiutils.axi4lite._ // FIXME
+    import chisel.axi.axi4lite._ // FIXME
     import chisel3._
 
     val dataWidthGen: Gen[DataWidth] = Gen.oneOf(Width32, Width64)