Make name_node() xstrdup its name argument

The name field of 'struct node' was really always supposed to be a
malloc()ed string, that is owned by the structure.  To avoid an extra
strdup() for strings coming up from the lexer, name_node() expects to take
uch an already malloc()ed string, which means it's not correct to pass it
a static string literal.

That's a pretty non-obvious constraint, so a bunch of incorrect uses have
crept in.  Really, avoiding the extra dup from the lexer isn't a big enough
benefit for this demonstrably dangerous interface.  So change it to do the
xstrdup() itself, removing the burden from callers.

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

dtc-parser.y

@@ -573,10 +573,12 @@ subnode:
 	  DT_PROPNODENAME nodedef
 		{
 			$$ = name_node($2, $1);
+			free($1);
 		}
 	| DT_DEL_NODE DT_PROPNODENAME ';'
 		{
 			$$ = name_node(build_node_delete(&@$), $2);
+			free($2);
 		}
 	| DT_OMIT_NO_REF subnode
 		{