The shadow stack space is == the number of register arguments
saved on stack, so reuse the same constant that is already defined.

Bug: v8:11879
Change-Id: I576c26770660de63c85089d658fcddc14bd5a08f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2997927Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75538}