x86, vdso: Move more vdso definitions into vdso.h

This fixes the Xen build and gets rid of a silly header file.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Stefani Seibold <stefani@seibold.net>
Link: http://lkml.kernel.org/r/1df77311795aff75f5742c787d277518314a38d3.1395366931.git.luto@amacapital.net


Signed-off-by: H. Peter Anvin <hpa@zytor.com>