devicetree: Add method to delete property by name

Will be used on Cavium SoC to delete devicetree entries that aren't
available with the board/configuration.

Change-Id: I7c58a2411206bca62d0e96fa627530e937383ac9
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/26693
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/include/device_tree.h

@@ -151,6 +151,8 @@ struct device_tree_node *dt_find_prop_value(struct device_tree_node *parent, con
 uint32_t dt_get_phandle(struct device_tree_node *node);
 // Write src into *dest as a 'length'-byte big-endian integer.
 void dt_write_int(u8 *dest, u64 src, size_t length);
+// Delete a property
+void dt_delete_prop(struct device_tree_node *node, const char *name);
 // Add different kinds of properties to a node, or update existing ones.
 void dt_add_bin_prop(struct device_tree_node *node, const char *name, void *data,
 		     size_t size);