net: atlantic: MACSec offload statistics HW bindings

This patch adds the Atlantic HW-specific bindings for MACSec statistics,
e.g. register addresses / structs, helper function, etc, which will be
used by actual callback implementations.

Signed-off-by: Dmitry Bogdanov <dbogdanov@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>