This change adds VLD2, VLD3, VLD4, VST2, VST3, VST4 (multiple structures)
for image or multi media optimazation.

Change-Id: Iae3538ef4434e436e3fb2f19153c58f918f773af
Reviewed-on: https://go-review.googlesource.com/c/go/+/166518
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>