octeontx2-pf: Enable PTP PPS output support

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>