dm: core: Support writing a boolean

Add functions to write a boolean property. This involves deleting it if
the value is false.

Add a new ofnode_has_property() as well. Add a comment about the behaviour
of of_read_property() when the property value is empty.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index a8605fb..ebea29d 100644
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -1037,11 +1037,20 @@
  * @node: node to read
  * @propname: property to read
  * @lenp: place to put length on success
- * Return: pointer to property, or NULL if not found
+ * Return: pointer to property value, or NULL if not found or empty
  */
 const void *ofnode_get_property(ofnode node, const char *propname, int *lenp);
 
 /**
+ * ofnode_has_property() - check if a node has a named property
+ *
+ * @node: node to read
+ * @propname: property to read
+ * Return: true if the property exists in the node, false if not
+ */
+bool ofnode_has_property(ofnode node, const char *propname);
+
+/**
  * ofnode_first_property()- get the reference of the first property
  *
  * Get reference to the first property of the node, it is used to iterate
@@ -1453,6 +1462,27 @@
 int ofnode_write_u32(ofnode node, const char *propname, u32 value);
 
 /**
+ * ofnode_write_bool() - Set a boolean property of an ofnode
+ *
+ * This either adds or deleted a property with a zero-length value
+ *
+ * @node:	The node for whose string property should be set
+ * @propname:	The name of the string property to set
+ * @value:	The new value of the boolean property
+ * Return: 0 if successful, -ve on error
+ */
+int ofnode_write_bool(ofnode node, const char *propname, bool value);
+
+/**
+ * ofnode_delete_prop() - Delete a property
+ *
+ * @node:	Node containing the property to delete
+ * @propname:	Name of property to delete
+ * Return: 0 if successful, -ve on error
+ */
+int ofnode_delete_prop(ofnode node, const char *propname);
+
+/**
  * ofnode_set_enabled() - Enable or disable a device tree node given by its
  *			  ofnode
  *