vceq(dst, dst, dst) does not seem to always set the register to all
ones. The right way should be be to use vmov (immediate) anyway. This
was not supported in the assembler yet, so we need changes to the
assembler, diassembler, and simulator.

There is an unfortunate fork in logic in the simulator, due to the way
the switches are set up, vmov (imm) logic is duplicated across two
different cases, because the switch looks at the top bit of the
immediate. Refactoring this will be a bigger change that is irrelevant
for this bug, so I'm putting that off for now. Instead we extract the
core of vmov (imm) into helpers and call it in the two cases.

Bug: chromium:1112124
Change-Id: I283dbcd86cb0572e5ee720835f897b51fae96701
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2337503
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69315}