net: atlantic: MACSec offload skeleton

This patch adds basic functionality for MACSec offloading for Atlantic
NICs.

MACSec offloading functionality is enabled if network card has
appropriate FW that has MACSec offloading enabled in config.

Actual functionality (ingress, egress, etc) will be added in follow-up
patches.

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>