net: Add support for mv88e609x switches

The Marvell Link Street mv88e60xx is a series of FastEthernet switch
chips, some of which also support Gigabit ports. It is similar to the
mv88e61xx series which support Gigabit on all ports.

The main difference is the number of ports. Which affects the
PORT_COUNT define and the size of the mask passed to
mv88e61xx_port_set_vlan().

Other than that it's just a matter of adding the appropriate chip
IDs.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Cc: Joshua Scott <joshua.scott@alliedtelesis.co.nz>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>