Add VSX instructions to perform add/sub/mul/div

R=jyan@ca.ibm.com, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com, danno@chromium.org, jkummerow@chromium.org, jochen@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2619763003
Cr-Commit-Position: refs/heads/master@{#42272}