net: phylink: Add PHYLINK_DEV operation type

In the PHYLINK_DEV operation type, the PHYLINK infrastructure can work
without an attached net_device. For printing usecases, instead, a struct
device * should be passed to PHYLINK using the phylink_config structure.

Also, netif_carrier_* calls ar guarded by the presence of a valid
net_device. When using the PHYLINK_DEV operation type, we cannot check
link status using the netif_carrier_ok() API so instead, keep an
internal state of the MAC and call mac_link_{down,up} only when the link
changed.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>