dcache fixes - all tests and ubmarks pass, hello world still broken

rocket/src/main/scala/consts.scala

@@ -23,6 +23,7 @@ object Constants
   val PC_PCR  = UFix(6, 4);
   val PC_MEM  = UFix(7, 4);
   val PC_MEM4 = UFix(8, 4);
+  val PC_EX   = UFix(9, 4);
 
   val KF_Y  = UFix(1, 1);
   val KF_N  = UFix(0, 1);