of: Add helpers to get one string in multiple strings property

Add of_property_read_string_index and of_property_count_strings
to retrieve one string inside a property that will contains
severals strings.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Kevin Hilman <khilman@ti.com>
diff --git a/include/linux/of.h b/include/linux/of.h
index 9180dc5..5dfe2d5 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -203,6 +203,11 @@
 extern int of_property_read_string(struct device_node *np,
 				   const char *propname,
 				   const char **out_string);
+extern int of_property_read_string_index(struct device_node *np,
+					 const char *propname,
+					 int index, const char **output);
+extern int of_property_count_strings(struct device_node *np,
+				     const char *propname);
 extern int of_device_is_compatible(const struct device_node *device,
 				   const char *);
 extern int of_device_is_available(const struct device_node *device);
@@ -256,6 +261,19 @@
 	return -ENOSYS;
 }
 
+static inline int of_property_read_string_index(struct device_node *np,
+						const char *propname, int index,
+						const char **out_string)
+{
+	return -ENOSYS;
+}
+
+static inline int of_property_count_strings(struct device_node *np,
+					    const char *propname)
+{
+	return -ENOSYS;
+}
+
 static inline const void *of_get_property(const struct device_node *node,
 				const char *name,
 				int *lenp)