This change adds vector multiply instructions to the assembler for
ppc64x.

Change-Id: I5143a2dc3736951344d43999066d38ab8be4a721
Reviewed-on: https://go-review.googlesource.com/107795Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>