x86: check kexec relocation code fits in a page

x86: check kexec relocation code fits in a page

The kexec relocation (control) code must fit in a single page so add a
link time check for this.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Don Slutz <dslutz@verizon.com>
Tested-by: Don Slutz <dslutz@verizon.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Daniel Kiper <daniel.kiper@oracle.com>
Acked-by: Keir Fraser <keir@xen.org>