net: dsa: bcm_sf2: add support for Wake-on-LAN

In order for Wake-on-LAN to work properly, we query the parent network
device Wake-on-LAN features and advertise those. Similarly, when
configuring Wake-on-LAN on a per-port network interface, we make sure
that we do not accept something the master network devices does not
support.

Finally, we need to maintain a bitmask of the ports enabled for
Wake-on-LAN to prevent the suspend() callback from disabling a port that
is used for waking up the system.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>