Due to ppc having a fixed 4 byte instruction length, changing
ByteChunk length from 8 to 4 bytes will fix any padding issues
while generating the "embed.S" file.

Change-Id: Ide799908effd88d5387e97627917b095fcc3051c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1524720
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60337}