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>

include/net/dsa.h

@@ -210,6 +210,12 @@ struct dsa_switch_driver {
 	void	(*get_ethtool_stats)(struct dsa_switch *ds,
 				     int port, uint64_t *data);
 	int	(*get_sset_count)(struct dsa_switch *ds);
+
+	/*
+	 * Suspend and resume
+	 */
+	int	(*suspend)(struct dsa_switch *ds);
+	int	(*resume)(struct dsa_switch *ds);
 };
 
 void register_switch_driver(struct dsa_switch_driver *type);