net: dsa: mv88e6xxx: add support for bridge flags

Add support for the bridge flags to Marvell 88e6xxx bridges, allowing
the multicast and unicast flood properties to be controlled.  These
can be controlled on a per-port basis via commands such as:

	bridge link set dev lan1 flood on|off
	bridge link set dev lan1 mcast_flood on|off

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>