Refactor vector register moves.

Eliminates code duplication, and moves between identical S registers
are elided.

Change-Id: Iec5d626c72f3c521a199a755e8804e26a5b4a782
Reviewed-on: https://chromium-review.googlesource.com/697946
Reviewed-by: Jim Stichnoth <stichnot@chromium.org>
2 files changed