net: fec: ptp: Enable PPS output based on ptp clock

net: fec: ptp: Enable PPS output based on ptp clock

FEC ptp timer has 4 channel compare/trigger function. It can be used to
enable pps output.
The pulse would be ouput high exactly on N second. The pulse ouput high
on compare event mode is used to produce pulse per second.  The pulse
width would be one cycle based on ptp timer clock source.Since 31-bit
ptp hardware timer is used, the timer will wrap more than 2 seconds. We
need to reload the compare compare event about every 1 second.

Signed-off-by: Luwei Zhou <b45643@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>