PowerPC specific sub-directories.

Technically, this is https://codereview.chromium.org/571173003/ from Andrew Low <andrew_low@ca.ibm.com>.

TBR=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/714093002

Cr-Commit-Position: refs/heads/master@{#25255}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25255 ce2b1a6d-e550-0410-aec6-3dcde31c8c00