net: atlantic: MACSec egress offload HW bindings

This patch adds the Atlantic HW-specific bindings for MACSec egress, 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>