net: lan966x: Implement SIOCSHWTSTAMP and SIOCGHWTSTAMP

Implement the ioctl callbacks SIOCSHWTSTAMP and SIOCGHWTSTAMP to allow
to configure the ports to enable/disable timestamping for TX. The RX
timestamping is always enabled. The HW is capable to run both 1-step
timestamping and 2-step timestamping.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>