fdt: Add a function to count strings

Given a device tree node and a property name, the fdt_count_strings()
function counts the number of strings found in the property value.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/libfdt.h b/include/libfdt.h
index a1ef1e1..cf97bf0 100644
--- a/include/libfdt.h
+++ b/include/libfdt.h
@@ -857,6 +857,15 @@
  */
 int fdt_stringlist_contains(const char *strlist, int listlen, const char *str);
 
+/**
+ * fdt_count_strings - count the number of strings in a string list
+ * @fdt: pointer to the device tree blob
+ * @node: offset of the node
+ * @property: name of the property containing the string list
+ * @return: the number of strings in the given property
+ */
+int fdt_count_strings(const void *fdt, int node, const char *property);
+
 /**********************************************************************/
 /* Read-only functions (addressing related)                           */
 /**********************************************************************/