The number of available double registers depends on supported CPU
features on arm. Any code that applies to all double regs must be
extra-careful to correctly handle either 16 or 32 registers.

This was not the case for deopt entries, which were recently moved
from a runtime-generated code stub to a mksnapshot-time-generated
builtin.

This CL fixes the issue by inspecting the runtime value of cpu
features and acting on it.

Bug: v8:8661,chromium:1142158
Change-Id: I6f4d2e6ee6a80217b9110194b8e1edbe8670d8d0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2498686
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70796}