To free up some ArchOpcode bits (especially for arm64), encode all
atomic opcodes that are duplicated between 32bit and 64bit widths with a
single opcode and encode the width in another field.

Bug: v8:12093
Change-Id: Ide05e8f0b2aa877ea776851e47df60dd410deae2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3093257Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76289}