power: Disable use of suspend-then-hibernate by default

This is just for the stable branch. In the unstable branch we probably want to revert the two relevant patches and hopefully get around to implement something saner for 3.32.

Unfortunately this feature is not ready for wider consumption. Also, we will need more invasive changes to properly fix this issue, which makes it hard to add a runtime option for it in the short term.

For this reason, revert the change again but leave a way to re-enable it at build time if it really is desired. See NEWS for more details.