dtoc: Process nodes to set up required properties

Add logic to assign property values to nodes as required by dtoc. The
references allow nodes to refer to each other in C code. The macros used
by dtoc are not yet defined in driver model. They will be added along
with the actual driver model implementation.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/src_scan.py b/tools/dtoc/src_scan.py
index bf3e5de..504dac0 100644
--- a/tools/dtoc/src_scan.py
+++ b/tools/dtoc/src_scan.py
@@ -188,6 +188,17 @@
         self._uclass = {}
         self._structs = {}
 
+    def get_driver(self, name):
+        """Get a driver given its name
+
+        Args:
+            name (str): Driver name
+
+        Returns:
+            Driver: Driver or None if not found
+        """
+        return self._drivers.get(name)
+
     def get_normalized_compat_name(self, node):
         """Get a node's normalized compat name