Shrink embedded.cc by writing out octa words instead of bytes. This
halves the size of the generated file from 28MB to 14MB in a debug build
and reduces compile times for the file from ~2s to ~0.6s.

Bug: v8:8129
Change-Id: I90893c7732d83f4eeedee964cd81958201e3b05c
Reviewed-on: https://chromium-review.googlesource.com/1204111Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55645}