gpsd: enable kpps support

GPSD has the ability to support KPPS. Its enablement is determined
primarily from the existence of `sys/timepps.h`. This file is provided
from the pps-tools package. Adjusting GPSD's Makefile to depend on the
pps-tools package if a developer has included pps-tools as part of a
build.

Signed-off-by: James Knight <james.knight@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>