Message type for PM_ time-related calls

Message type for PM_ time-related calls

 - Message type for PM_CLOCK_SETTIME, PM_CLOCK_GETTIME,
   PM_CLOCK_GETRES, PM_GETTIMEOFDAY, PM_SETTIME.

 - Small adaptation, message only transfert sub-second time in
   nanoseconds, instead of both nano- and micro-seconds. Conversion
   is done in userland, as required.

Change-Id: Ie4a6e0c457cc12626e85d2102c086a95311cf3e7