With AVX, we don't need to force dst to be the same as first operand,
this can eliminate some moves.

(On the js file in linked bug, we can eliminate all movs before shifts,
saving ~20 movs.)

Bug: v8:10116
Change-Id: I7951b5d8e42995098ddee2a326d0fe6f183c0fb9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2477494
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70581}