libfdt: Add functions for handling the "compatible" property

This patch adds functions for dealing with the compatible property.
fdt_node_check_compatible() can be used to determine whether a node is
compatible with a given string and fdt_node_offset_by_compatible()
locates nodes with a given compatible string.

Testcases for these functions are also included.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/tests/Makefile.tests b/tests/Makefile.tests
index c84b63d..3c3305b 100644
--- a/tests/Makefile.tests
+++ b/tests/Makefile.tests
@@ -2,6 +2,7 @@
 	root_node find_property subnode_offset path_offset \
 	get_name getprop get_path supernode_atdepth_offset parent_offset \
 	node_offset_by_prop_value \
+	node_check_compatible node_offset_by_compatible \
 	notfound \
 	setprop_inplace nop_property nop_node \
 	sw_tree1 \