net/mlx5e: Move MACsec flow steering operations to be used as core library

Move MACsec flow steering operations(macsec_fs) from core/en_accel to
core/lib, this mandates moving MACsec statistics structure from the
general MACsec code header(en_accel/macsec.h) to macsec_fs header to
remove macsec_fs.h dependency over en_accel/macsec.h.

This to lay the ground for RoCE MACsec by moving all the data
that will need to be accessed by both ethernet MACsec and
RoCE MACsec to be shared at core.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>