OF: add empty of_device_is_available for !OF

Add an empty version of of_device_is_available.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

include/linux/of.h

@@ -379,6 +379,11 @@ static inline int of_device_is_compatible(const struct device_node *device,
 	return 0;
 }
 
+static inline int of_device_is_available(const struct device_node *device)
+{
+	return 0;
+}
+
 static inline struct property *of_find_property(const struct device_node *np,
 						const char *name,
 						int *lenp)