net: dsa: allow switch drivers to implement suspend/resume hooks

Add an abstraction layer to suspend/resume switch devices, doing the
following split:

- suspend/resume the slave network devices and their corresponding PHY
  devices
- suspend/resume the switch hardware using switch driver callbacks

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 f90899e..dc9756d 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -56,6 +56,8 @@
 struct net_device *dsa_slave_create(struct dsa_switch *ds,
 				    struct device *parent,
 				    int port, char *name);
+int dsa_slave_suspend(struct net_device *slave_dev);
+int dsa_slave_resume(struct net_device *slave_dev);
 
 /* tag_dsa.c */
 extern const struct dsa_device_ops dsa_netdev_ops;