net: ethernet: ti: cpsw: enable HWTSTAMP_FILTER_PTP_V1_L4_EVENT filter

CPSW driver supports PTP v1 messages, but for unknown reasons this filter
is not advertised. As result,
./tools/testing/selftests/networking/timestamping/timestamping utility
can't be used for testing of CPSW RX timestamping with option
SOF_TIMESTAMPING_RX_HARDWARE, because it uses
HWTSTAMP_FILTER_PTP_V1_L4_SYNC filter.

Hence, fix it by advertising HWTSTAMP_FILTER_PTP_V1_L4_XXX filters
in CPSW driver.

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