uclass: Add dev_get_uclass_index() to get the uclass/index of a device

This function is the reciprocal of uclass_find_device().
It will be used to print the index information in dm tree dump.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index d609b17..3113d6a 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -171,6 +171,27 @@
 	return UCLASS_INVALID;
 }
 
+int dev_get_uclass_index(struct udevice *dev, struct uclass **ucp)
+{
+	struct udevice *iter;
+	struct uclass *uc = dev->uclass;
+	int i = 0;
+
+	if (list_empty(&uc->dev_head))
+		return -ENODEV;
+
+	list_for_each_entry(iter, &uc->dev_head, uclass_node) {
+		if (iter == dev) {
+			if (ucp)
+				*ucp = uc;
+			return i;
+		}
+		i++;
+	}
+
+	return -ENODEV;
+}
+
 int uclass_find_device(enum uclass_id id, int index, struct udevice **devp)
 {
 	struct uclass *uc;