For i64x2.ext_mul and i16x8.ext_mul, we can simply call the
macro-assembler functions.

For i32x4.ext_mul, the macro-assembler requires that dst == src1 if AVX
is not supported, so we add a helper function to do that check, and make
sure dst == src1 before calling into macro-assembler.

Bug: v8:11262
Change-Id: Iff8e99967f4ab157021d0706e0142df894468142
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2603765Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71903}