Add comment for relocations MO_HIGHER and HIGHEST in MipsBaseInfo.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160636 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MCTargetDesc/MipsBaseInfo.h

@@ -81,6 +81,8 @@ namespace MipsII {
     MO_GOT_PAGE,
     MO_GOT_OFST,
 
+    /// MO_HIGHER/HIGHEST - Represents the highest or higher half word of a
+    /// 64-bit symbol address.
     MO_HIGHER,
     MO_HIGHEST
   };