net: dsa: bcm_sf2: force link for all fixed PHY devices

For ports of the switch that we define as "fixed PHYs" such as MoCA, we
would have our Port 7 special handling that would allow us to assert the
link status indication.

For other ports, such as e.g: RGMII_1 connected to a cable modem, we
would rely on whatever the bootloader has left configured, which is a
bad assumption to make, we really need to force the link status
indication here.

Fixes: 246d7f77 ("net: dsa: add Broadcom SF2 switch driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>