binman: Allow entry types to override FDT contents

At present the contents of an FDT (for each phase) are fixed,
determined by the build and provided to Binman as input files.

Provide a means for entry types to provide their own FDT, so that it can
be processed, if needed.

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

tools/binman/entry.py

@@ -1386,3 +1386,15 @@ features to produce new behaviours.
 
     def UpdateSignatures(self, privatekey_fname, algo, input_fname):
         self.Raise('Updating signatures is not supported with this entry type')
+
+    def FdtContents(self, fdt_etype):
+        """Get the contents of an FDT for a particular phase
+
+        Args:
+            fdt_etype (str): Filename of the phase of the FDT to return, e.g.
+                'u-boot-tpl-dtb'
+
+        Returns:
+            bytes: Contents of requested FDT
+        """
+        return self.section.FdtContents(fdt_etype)

tools/binman/etype/blob_dtb.py

@@ -41,12 +41,12 @@ class Entry_blob_dtb(Entry_blob):
     def ObtainContents(self, fake_size=0):
         """Get the device-tree from the list held by the 'state' module"""
         self._filename = self.GetDefaultFilename()
-        self._pathname, _ = state.GetFdtContents(self.GetFdtEtype())
+        self._pathname, _ = self.FdtContents(self.GetFdtEtype())
         return super().ReadBlobContents()
 
     def ProcessContents(self):
         """Re-read the DTB contents so that we get any calculated properties"""
-        _, indata = state.GetFdtContents(self.GetFdtEtype())
+        _, indata = self.FdtContents(self.GetFdtEtype())
 
         if self.compress == 'zstd' and self.prepend != 'length':
             self.Raise('The zstd compression requires a length header')

tools/binman/image.py

@@ -425,3 +425,7 @@ class Image(section.Entry_section):
         super().AddBintools(bintools)
         self.bintools = bintools
         return bintools
+
+    def FdtContents(self, fdt_etype):
+        """This base-class implementation simply calls the state function"""
+        return state.GetFdtContents(fdt_etype)