dtoc: Create a base class for Fdt

At present we have two separate implementations of the Fdt library, one which
uses fdtget/fdtput and one which uses libfdt (via swig).

Before adding more functionality it makes sense to create a base class for
these. This will allow common functions to be shared, and make the Fdt API
a little clearer.

Create a new fdt.py file with the base class, and adjust fdt_normal.py and
fdt_fallback.py to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/dtoc/fdt.py

@@ -0,0 +1,68 @@
+#!/usr/bin/python
+#
+# Copyright (C) 2016 Google, Inc
+# Written by Simon Glass <sjg@chromium.org>
+#
+# SPDX-License-Identifier:      GPL-2.0+
+#
+
+import struct
+import sys
+
+import fdt_util
+
+# This deals with a device tree, presenting it as an assortment of Node and
+# Prop objects, representing nodes and properties, respectively. This file
+# contains the base classes and defines the high-level API. Most of the
+# implementation is in the FdtFallback and FdtNormal subclasses. See
+# fdt_select.py for how to create an Fdt object.
+
+def CheckErr(errnum, msg):
+    if errnum:
+        raise ValueError('Error %d: %s: %s' %
+            (errnum, libfdt.fdt_strerror(errnum), msg))
+
+class PropBase:
+    """A device tree property
+
+    Properties:
+        name: Property name (as per the device tree)
+        value: Property value as a string of bytes, or a list of strings of
+            bytes
+        type: Value type
+    """
+    def __init__(self, node, offset, name):
+        self._node = node
+        self._offset = offset
+        self.name = name
+        self.value = None
+
+class NodeBase:
+    """A device tree node
+
+    Properties:
+        offset: Integer offset in the device tree
+        name: Device tree node tname
+        path: Full path to node, along with the node name itself
+        _fdt: Device tree object
+        subnodes: A list of subnodes for this node, each a Node object
+        props: A dict of properties for this node, each a Prop object.
+            Keyed by property name
+    """
+    def __init__(self, fdt, offset, name, path):
+        self._fdt = fdt
+        self._offset = offset
+        self.name = name
+        self.path = path
+        self.subnodes = []
+        self.props = {}
+
+class Fdt:
+    """Provides simple access to a flat device tree blob.
+
+    Properties:
+      fname: Filename of fdt
+      _root: Root of device tree (a Node object)
+    """
+    def __init__(self, fname):
+        self._fname = fname