todr_settime_ymdhms. This allows drivers to avoid repeated conversions, and
allows us to centralize check for Y2038 overflow. As discussed on
tech-kern.
1) don't set a clock when panicing during early boot
2) if the filesystem time is newer than the rtc time (by at least 2 days) then
revert to the filesystem time.
3) use x86 style messaging.
We still use a threshold of 2 days of gain or loss in time to warn though.
