Add summary statistics.

Add new options to ptp4l and phc2sys to print summary statistics of the
clock instead of the individual samples.

[ RC - Fix () function prototype with (void).
     - Use unsigned for sample counter.
     - Fix over-zealous line breaks. ]

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>