ptp: ocp: adjust utc_tai_offset to TOD info

utc_tai_offset is used to correct IRIG, DCF and NMEA outputs and is
set during initialisation but is not corrected during leap second
announce event.  Add watchdog code to control this correction.

Signed-off-by: Vadim Fedorenko <vadfed@fb.com>
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>