x86_64: vdso.lds in arch/x86_64/vdso/.gitignore

Create arch/x86_64/vdso/.gitignore and put vdso.lds into it.

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>