net: dsa: mv88e6xxx: populate supported_interfaces and mac_capabilities

Populate the supported interfaces and MAC capabilities for the
Marvell MV88E6xxx DSA switches in preparation to using these for the
validation functionality.

Patch co-authored by Marek.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Marek Behún <kabel@kernel.org> [ fixed 6341 and 6393x ]
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>