net: lan966x: convert to ndo_hwtstamp_get() and ndo_hwtstamp_set()

The hardware timestamping through ndo_eth_ioctl() is going away.
Convert the lan966x driver to the new API before that can be removed.

After removing the timestamping logic from lan966x_port_ioctl(), the
rest is equivalent to phy_do_ioctl().

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20230801142824.1772134-10-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>