Optimize initial implementation of i32_eqz and implement i64_eqz.

Bug: v8:6600
Change-Id: I695454a160fc57dc9981725583ed2f27c2c537db
Reviewed-on: https://chromium-review.googlesource.com/978207Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#52189}