Register the two (leapSecond info and timestamp) at exactly the
same time. Still not perfect but better than before.

FMC DIO device supports leap seconds fields for the timestamps. A new
usr-timestamp type has been created to deal with differences between timespec
and new FMC DIO timestamps.
- New fields for leap-seconds in fmc-dio-device driver
- Create usr-timestamp type for irq-demo
- Conversion mechanism from fmc-dio timestamp to usr-timestamp