In order to support PTP in FDMA, PTP handling code is needed. Since
this is the same as for register-based extraction, export it with
a new ocelot_ptp_rx_timestamp() function.
Reviewed-by: NVladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: NClément Léger <clement.leger@bootlin.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>