Implement 64 bit multiply in mips32 and, in addition, add the lo/hi registers which are also used for other 64 bit math such as div, rem.
BUG=
R=jpp@chromium.org, stichnot@chromium.org
Review URL: https://codereview.chromium.org/1716483003 .
Patch from Reed Kotler <rkotlerimgtec@gmail.com>.
