PTP block supports generating PPS output signal on GPIO pin. This patch
adds the support in the PTP PHC driver using standard periodic output
interface.

User can enable/disable/configure PPS by writing to the below sysfs entry

echo perout.index start.sec start.nsec period.sec period.nsec >
/sys/class/ptp/ptp0/period

Example to generate 50% duty cycle PPS signal:
echo 0 0 0 0 500000000 >  /sys/class/ptp/ptp0/period
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>