x86_64: increase VDSO_TEXT_OFFSET for ancient binutils

For some reason old binutils genertate larger headers so increase the text
offset of the vdso to avoid linker errors.

Roland McGrath explains:
  "There are extra symbols in the '.dynsym' section that are responsible
   for the size difference (They also cause corresponding inflation in
   '.gnu.version')

   Older ld's wrongly generated these unneeded symbols in .dynsym.  This
   was fixed not all that long ago (2006); binutils-2.17.50.0.6 might be
   the first fixed version, but I have not verified for sure where the
   cutoff was.

   The unneeded symbols et al from old ld add almost 700 bytes excess.
   This limits fairly tightly the amount by which the actual text and
   data in the vDSO can grow in the future without pushing the whole
   file over 4kb.  If it does grow later on, we should consider changing
   the layout with a config option or something to pack it better
   without that padding, when building the kernel with newer binutils."

Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Roland McGrath <roland@redhat.com>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>