Merge the SSE and AVX opcodes for I16x8Eq and I16x8GtS. We delegate to
the macro-assembler to check for AVX.

No functionality change is expected.

Bug: v8:11217
Change-Id: I873b261d6f949bfc6755fe4c0e09b964a02c3684
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3131371
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76737}