gpsd: add deterministic support for KPPS interface

gpsd enables low-precision PPS (pulse-per-second) support by default,
but only includes the high-precision kernel API capabilities if
sys/timepps.h is also detected.  Under Linux the pps-tools package
installs this header.  Remove the feature non-determinism and increase
gpsd capabilities by adding an explicit dependency.

See: http://www.catb.org/gpsd/gpsd-time-service-howto.html#_enabling_pps



Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>