Binaries: add ppc64 and ppc64le

[harding]

22.0 adds two new binaries; this adds them to the download page. Preview:

Travis is dead, but my local tests pass and they include a test to ensure all class="dl" links on the Download page point to downloadable files.

```text $ make bundle exec jekyll clean Configuration file: /home/harding/bitcoincore.org/_config.yml Cleaner: Removing /home/harding/bitcoincore.org/_site... Cleaner: Removing /home/harding/bitcoincore.org/.jekyll-metadata... Cleaner: Removing .sass-cache... bundle exec jekyll build --future --drafts --unpublished Configuration file: /home/harding/bitcoincore.org/_config.yml Source: /home/harding/bitcoincore.org Destination: /home/harding/bitcoincore.org/_site Incremental build: disabled. Enable with --incremental Generating... done in 64.248 seconds. Auto-regeneration: disabled. Use --watch to enable. ## Check for broken Markdown reference-style links that are displayed in text unchanged, e.g. [broken][broken link] ! find _site/ -name '*.html' | xargs grep ']\[' | grep -v skip-test | grep . ## Check for malformed HTML and broken internal links bash -c "set -o pipefail ; bundle exec htmlproofer --check-html --disable-external --url-ignore '/^\/bin/.*/' ./_site | cat" Running ["LinkCheck", "ScriptCheck", "ImageCheck", "HtmlCheck"] on ["./_site"] on *.html... Ran on 1421 files! HTML-Proofer finished successfully. ## Check that links on the /en/download page point to the separately-stored binaries in /bin contrib/qa/test-binary-availability.sh && echo "SUCCESS checking URLs for binaries" SUCCESS checking URLs for binaries ```

[harding]

Thanks @fanquake for reporting!

[fanquake]

LGTM. No opinion on the logo, probably just important to get the newer binaries up on the download page for now.