ppbus: Set the lock for pps interface, update to latest api

Since we take a lock when we enter the ioctl, we need to set driver_mtx
in the pps structure so it can be dropped while sleeping during a call
to timepps_fetch() with a non-zero timeout (PPS_CANWAIT feature).

MFC After: 5 days
Sponsored by: Netflix
Reviewed by: ian
Differential Revision: https://reviews.freebsd.org/D31763