net: dsa: Make most functions take a dsa_port argument

In preparation for allowing platform data, and therefore no valid
device_node pointer, make most DSA functions takes a pointer to a
dsa_port structure whenever possible. While at it, introduce a
dsa_port_is_valid() helper function which checks whether port->dn is
NULL or not at the moment.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 63ae148..16194a4 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -50,8 +50,8 @@ struct dsa_slave_priv {
 
 /* dsa.c */
 int dsa_cpu_dsa_setup(struct dsa_switch *ds, struct device *dev,
-		      struct device_node *port_dn, int port);
-void dsa_cpu_dsa_destroy(struct device_node *port_dn);
+		      struct dsa_port *dport, int port);
+void dsa_cpu_dsa_destroy(struct dsa_port *dport);
 const struct dsa_device_ops *dsa_resolve_tag_protocol(int tag_protocol);
 int dsa_cpu_port_ethtool_setup(struct dsa_switch *ds);
 void dsa_cpu_port_ethtool_restore(struct dsa_switch *ds);