binman: cbfs: Refactor the init process

Update the constructor to work in the recommended way, where the node
properties are read in a separate function. This makes it more similar to
entry_Section.

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

tools/binman/etype/cbfs.py

@@ -168,12 +168,16 @@ class Entry_cbfs(Entry):
         from binman import state
 
         super().__init__(section, etype, node)
-        self._cbfs_arg = fdt_util.GetString(node, 'cbfs-arch', 'x86')
         self.align_default = None
         self._entries = OrderedDict()
-        self.ReadEntries()
         self.reader = None
 
+    def ReadNode(self):
+        """Read properties from the atf-fip node"""
+        super().ReadNode()
+        self._cbfs_arg = fdt_util.GetString(self._node, 'cbfs-arch', 'x86')
+        self.ReadEntries()
+
     def ReadEntries(self):
         """Read the subnodes to find out what should go in this CBFS"""
         for node in self._node.subnodes: