dm: core: Add ofnode_read_string_count()

This provides a way to find the number of strings in a string list. Add it
and also fix up the comment for ofnode_read_string_index().

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1
diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index 149622a..d261a61 100644
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -359,7 +359,7 @@
 			     const char *string);
 
 /**
- * fdt_stringlist_get() - obtain the string at a given index in a string list
+ * ofnode_read_string_index() - obtain an indexed string from a string list
  *
  * Note that this will successfully extract strings from properties with
  * non-NUL-terminated values. For example on small-valued cell properties
@@ -380,6 +380,16 @@
 			     const char **outp);
 
 /**
+ * ofnode_read_string_count() - find the number of strings in a string list
+ *
+ * @node: node to check
+ * @propname: name of the property containing the string list
+ * @return:
+ *   number of strings in the list, or -ve error value if not found
+ */
+int ofnode_read_string_count(ofnode node, const char *property);
+
+/**
  * ofnode_parse_phandle_with_args() - Find a node pointed by phandle in a list
  *
  * This function is useful to parse lists of phandles and their arguments.