dt: add empty of_alias_get_id() for non-dt builds

Add function of_alias_get_id() reporting -ENOSYS
for non-dt builds, so that drivers migrating to dt
can save some '#ifdef CONFIG_OF'.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: NRob Herring <rob.herring@calxeda.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

include/linux/of.h

@@ -303,6 +303,11 @@ static inline struct device_node *of_parse_phandle(struct device_node *np,
 	return NULL;
 }
 
+static inline int of_alias_get_id(struct device_node *np, const char *stem)
+{
+	return -ENOSYS;
+}
+
 #define of_match_ptr(_ptr)	NULL
 #define of_match_node(_matches, _node)	NULL
 #endif /* CONFIG_OF */