dm: core: Allow writing to a flat tree with ofnode

In generally it is not permitted to implement an ofnode function only for
flat tree or live tree. Both must be supported. Also the code for
live tree access should be in of_access.c rather than ofnode.c which is
really just for holding the API-conversion code.

Update ofnode_write_prop() accordingly and fix the test so it can work
with flat tree too.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dm/of_access.h

@@ -519,4 +519,16 @@ int of_alias_get_highest_id(const char *stem);
  */
 struct device_node *of_get_stdout(void);
 
+/**
+ * of_write_prop() - Write a property to the device tree
+ *
+ * @np:		device node to which the property value is to be written
+ * @propname:	name of the property to write
+ * @value:	value of the property
+ * @len:	length of the property in bytes
+ * Returns: 0 if OK, -ve on error
+ */
+int of_write_prop(struct device_node *np, const char *propname, int len,
+		  const void *value);
+
 #endif

include/dm/ofnode.h

@@ -44,6 +44,24 @@ static inline const struct device_node *ofnode_to_np(ofnode node)
 	return node.np;
 }
 
+/**
+ * ofnode_to_npw() - convert an ofnode to a writeable live DT node pointer
+ *
+ * This cannot be called if the reference contains an offset.
+ *
+ * @node: Reference containing struct device_node * (possibly invalid)
+ * Return: pointer to device node (can be NULL)
+ */
+static inline struct device_node *ofnode_to_npw(ofnode node)
+{
+#ifdef OF_CHECKS
+	if (!of_live_active())
+		return NULL;
+#endif
+	/* Drop constant */
+	return (struct device_node *)node.np;
+}
+
 /**
  * ofnode_to_offset() - convert an ofnode to a flat DT offset
  *