libfdt: Make fdtdec_get_child_count() available for HOST

The tool need to use fdtdec_get_child_count(), make it available for
HOST_CC.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Punit Agrawal <punit1.agrawal@toshiba.co.jp>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/fdtdec_common.c b/lib/fdtdec_common.c
index 088e9e9..5775992 100644
--- a/lib/fdtdec_common.c
+++ b/lib/fdtdec_common.c
@@ -53,3 +53,14 @@
 	debug("(not found)\n");
 	return default_val;
 }
+
+int fdtdec_get_child_count(const void *blob, int node)
+{
+	int subnode;
+	int num = 0;
+
+	fdt_for_each_subnode(subnode, blob, node)
+		num++;
+
+	return num;
+}