We can have more optimizations for this instruction, they leave some
junk in the top lanes of dst, but that doesn't matter:

- when lane is 1: we use movshdup, this is 4 bytes long
- when lane is 2: use movhlps, this is 3 bytes long
- otherwise use shufps (4 bytes) or pshufd (5 bytes)

All of which are better than insertps (6 bytes).

Change-Id: I0e524431d1832e297e8c8bb418d42382d93fa691
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2591850
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71813}