dm: core: Add function to get child count of ofnode or device

This patch add function used to get the child count of
a ofnode or a device

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/ofnode.c b/drivers/core/ofnode.c
index 20871a6..e3c42da 100644
--- a/drivers/core/ofnode.c
+++ b/drivers/core/ofnode.c
@@ -474,6 +474,17 @@
 	return ofnode_path(prop);
 }
 
+int ofnode_get_child_count(ofnode parent)
+{
+	ofnode child;
+	int num = 0;
+
+	ofnode_for_each_subnode(child, parent)
+		num++;
+
+	return num;
+}
+
 static int decode_timing_property(ofnode node, const char *name,
 				  struct timing_entry *result)
 {