binman: Add a ProcessFdt() method

Some entry types modify the device tree, e.g. to remove microcode or add a
property. So far this just modifies their local copy and does not affect
a 'shared' device tree.

Rather than doing this modification in the ObtainContents() method, and a
new ProcessFdt() method which is specifically designed to modify this
shared device tree.

Move the existing device-tree code over to use this method, reducing
ObtainContents() to the goal of just obtaining the contents without any
processing, even for device tree.

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

tools/binman/entry.py

@@ -130,6 +130,9 @@ class Entry(object):
         self.align_end = fdt_util.GetInt(self._node, 'align-end')
         self.pos_unset = fdt_util.GetBool(self._node, 'pos-unset')
 
+    def ProcessFdt(self, fdt):
+        return True
+
     def SetPrefix(self, prefix):
         """Set the name prefix for a node