Several users have commented (via filing PRs) that having ntp* depend
on devfs is useful so that a hardware time device can start with its
necessary device nodes already in place. While this ordering happens
as a side effect currently in HEAD, and the PRs were generally fixed
via upgrades, etc; it's better to make it explicit.

While I'm here, ntpd should REQUIRE ntpdate, rather than ntpdate
using BEFORE: ntpd.