dm: core: Add functions to find parent and OF data

Add dev_get_parent() as a convenience to obtain the parent of a device.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@ti.com>
Acked-by: Heiko Schocher <hs@denx.de>
diff --git a/include/dm/device.h b/include/dm/device.h
index 287504c..13598a1 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -208,6 +208,14 @@
 void *dev_get_priv(struct udevice *dev);
 
 /**
+ * struct dev_get_parent() - Get the parent of a device
+ *
+ * @child:	Child to check
+ * @return parent of child, or NULL if this is the root device
+ */
+struct udevice *dev_get_parent(struct udevice *child);
+
+/**
  * dev_get_of_data() - get the device tree data used to bind a device
  *
  * When a device is bound using a device tree node, it matches a