Add OF_xref_from_node_strict() which returns -1 if there is no xref handle

for the node.  The default routine returns the untranslated handle, which
is sometimes useful, but sometimes you really need to know there's no
entry in the xref<->node<->device translation table.

sys/dev/ofw/openfirm.c

@@ -554,15 +554,15 @@ OF_node_from_xref(phandle_t xref)
 	return (node);
 }
 
-phandle_t
-OF_xref_from_node(phandle_t node)
+static phandle_t
+xref_from_node(phandle_t node, phandle_t notfoundvalue)
 {
 	struct xrefinfo *xi;
 	phandle_t xref;
 
 	if (xref_init_done) {
 		if ((xi = xrefinfo_find(node, FIND_BY_NODE)) == NULL)
-			return (node);
+			return (notfoundvalue);
 		return (xi->xref);
 	}
 
@@ -570,10 +570,24 @@ OF_xref_from_node(phandle_t node)
 	    -1 && OF_getencprop(node, "ibm,phandle", &xref,
 	    sizeof(xref)) == -1 && OF_getencprop(node,
 	    "linux,phandle", &xref, sizeof(xref)) == -1)
-		return (node);
+		return (notfoundvalue);
 	return (xref);
 }
 
+phandle_t
+OF_xref_from_node(phandle_t node)
+{
+
+	return (xref_from_node(node, node));
+}
+
+phandle_t
+OF_xref_from_node_strict(phandle_t node)
+{
+
+	return (xref_from_node(node, -1));
+}
+
 device_t
 OF_device_from_xref(phandle_t xref)
 {

sys/dev/ofw/openfirm.h

@@ -128,10 +128,12 @@ ssize_t		OF_package_to_path(phandle_t node, char *buf, size_t len);
  * Some OF implementations (IBM, FDT) have a concept of effective phandles
  * used for device-tree cross-references. Given one of these, returns the
  * real phandle. If one can't be found (or running on OF implementations
- * without this property), returns its input.
+ * without this property), OF_xref_from_node() returns its input, while the
+ * strict version returns -1.
  */
 phandle_t	OF_node_from_xref(phandle_t xref);
 phandle_t	OF_xref_from_node(phandle_t node);
+phandle_t	OF_xref_from_node_strict(phandle_t node);
 
 /*
  * When properties contain references to other nodes using xref handles it is