Update header includes for ported src/register/ code

Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
Change-Id: I8a56d8119549717f96ae49eb1c1ba8d041e04914
diff --git a/src/register/prdfRegisterCache.H b/src/register/prdfRegisterCache.H
index be34884..995ab03 100644
--- a/src/register/prdfRegisterCache.H
+++ b/src/register/prdfRegisterCache.H
@@ -29,14 +29,14 @@
 /** @file prdfRegisterCache.H */
 
 #include <map>
-#include <iipbits.h>
+
+#include <util/hei_bit_string.hpp>
+
 #include <prdfGlobal.H>
 #include <prdfScanFacility.H>
 #include <prdfScomRegisterAccess.H>
 #include <prdfTargetFwdRef.H>
 
-class BitString;
-
 namespace PRDF
 {
 /**