fix doxygen brief in subzero header files

src/IceRegistersX8664.h

 //===- subzero/src/IceRegistersX8664.h - Register information ---*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file declares the registers and their encodings for x86-64.
+/// \brief Declares the registers and their encodings for x86-64.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEREGISTERSX8664_H
 #define SUBZERO_SRC_ICEREGISTERSX8664_H
 
 #include "IceDefs.h"
 #include "IceInstX8664.def"
 #include "IceTypes.h"
 
@@ skipping 46 matching lines @@
   Encoded_8_##val = encode,
     REGX8664_BYTEREG_TABLE
 #undef X
         Encoded_Not_ByteReg = -1
   };
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEREGISTERSX8664_H