net: atlantic: PTP statistics

This patch adds PTP rings statistics. Before that
these were missing from overall stats, hardening debugging
and analysis.

Signed-off-by: Pavel Belous <pbelous@marvell.com>
Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>