libfdt: Add fdt_node_offset_by_prop_value()

This patch adds a function to libfdt to locate nodes containing a
property with a specific value.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -40,6 +40,7 @@ tree1_tests () {
     run_test get_path $TREE
     run_test supernode_atdepth_offset $TREE
     run_test parent_offset $TREE
+    run_test node_offset_by_prop_value $TREE
     run_test notfound $TREE
 
     # Write-in-place tests