net: mscc: ocelot: deinitialize only initialized ports

Currently mscc_ocelot_init_ports() will skip initializing a port when it
doesn't have a phy-handle, so the ocelot->ports[port] pointer will be
NULL. Take this into consideration when tearing down the driver, and add
a new function ocelot_deinit_port() to the switch library, mirror of
ocelot_init_port(), which needs to be called by the driver for all ports
it has initialized.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>