ELF: Remove <Arch>TargetHandler::kindString.

<Arch>TargetHandler::kindString is a static member variable
containg a list of names of relocation types.

The member is used only by one function, registerRelocationNames,
so they don't have to be a static member.

This patch makes the visibility of the data narrower by making
them file-scoped variables in small files.

llvm-svn: 233867