This CL is the first in a series of work that will remove ebx (the new
kRootRegister) use from all ia32 ASM builtins and stubs.

Bug: v8:6666
Change-Id: If417f1194a27ddae9e38d50e0a651dfc129e8b05
Reviewed-on: https://chromium-review.googlesource.com/1230095Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56000}