[elf2yaml][ELF] Move Info field to the RelocationSection structure. This
field represents ELF section header sh_info field and does not have any
sense for regular sections. Its interpretation depends on section type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209801 91177308-0d34-0410-b5e6-96231b3b80d8