net: dsa: mv88e6xxx: Support jumbo configuration on 6190/6190X

The MV88E6190 and MV88E6190X both support per port jumbo configuration
just like the other GE switches. Install the appropriate ops.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>