improved error returns for hipHostRegister/UnRegister functions

include/hip_runtime_api.h

@@ -159,6 +159,8 @@ typedef enum hipError_t {
     ,hipErrorPeerAccessAlreadyEnabled ///< Peer access was already enabled from the current device.
     ,hipErrorRuntimeMemory            ///< HSA runtime memory call returned error.  Typically not seen in production systems.
     ,hipErrorRuntimeOther             ///< HSA runtime call other than memory returned error.  Typically not seen in production systems.
+    ,hipErrorHostMemoryAlreadyRegistered ///< Produced when trying to lock a page-locked memory.
+    ,hipErrorHostMemoryNotRegistered  ///< Produced when trying to unlock a non-page-locked memory.
     ,hipErrorTbd                      ///< Marker that more error codes are needed.
 } hipError_t;