powerpc/windfarm: const'ify and add "priv" field to controls & sensors

const'ify the sensor ops and name and add a void* for use by
the control and sensor drivers to point back to their private
data, avoiding the need to create a wrapper data structure
per sensor or control instance.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/macintosh/windfarm.h

@@ -36,8 +36,8 @@ struct wf_control_ops {
 
 struct wf_control {
 	struct list_head		link;
-	struct wf_control_ops	*ops;
-	char			*name;
+	const struct wf_control_ops	*ops;
+	const char			*name;
 	int				type;
 	struct kref			ref;
 	struct device_attribute		attr;
@@ -86,10 +86,11 @@ struct wf_sensor_ops {
 
 struct wf_sensor {
 	struct list_head		link;
-	struct wf_sensor_ops	*ops;
-	char			*name;
+	const struct wf_sensor_ops	*ops;
+	const char			*name;
 	struct kref			ref;
 	struct device_attribute		attr;
+	void				*priv;
 };
 
 /* Same lifetime rules as controls */