Add support for Embedded Constant Pools for PPC and Arm

Add support for Embedded Constant Pools for PPC and Arm

Embed constant pools within their corresponding Code
objects.

This removes support for out-of-line constant pools in favor
of the new approach -- the main advantage being that it
eliminates the need to allocate and manage separate constant
pool array objects.

Currently supported on PPC and ARM.  Enabled by default on
PPC only.

This yields a 6% improvment in Octane on PPC64.

R=bmeurer@chromium.org, rmcilroy@chromium.org, michael_dawson@ca.ibm.com
BUG=chromium:478811
LOG=Y

Review URL: https://codereview.chromium.org/1162993006

Cr-Commit-Position: refs/heads/master@{#28801}