fdt: introduce fdtdec_get_child_count

Introduce fdtdec_get_child_count for get the number of subnodes
of one parent node.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/fdtdec.c b/lib/fdtdec.c
index 0eb56af..1b1ca02 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -831,6 +831,17 @@
 	return rc;
 }
 
+int fdtdec_get_child_count(const void *blob, int node)
+{
+	int subnode;
+	int num = 0;
+
+	fdt_for_each_subnode(blob, subnode, node)
+		num++;
+
+	return num;
+}
+
 int fdtdec_get_byte_array(const void *blob, int node, const char *prop_name,
 		u8 *array, int count)
 {