net: ethernet: ti: am65-cpsw-nuss: enable packet timestamping support

The MCU CPSW Common Platform Time Sync (CPTS) provides possibility to
timestamp TX PTP packets and all RX packets.

This enables corresponding support in TI AM65x/J721E MCU CPSW driver.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>