binman: Forward AddBintools calls to sub entries in cbfs_util

Forward AddBintools calls to sub entries in cbfs_util to collect
bintools of sub entries.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/etype/cbfs.py b/tools/binman/etype/cbfs.py
index 4a1837f..832f8d0 100644
--- a/tools/binman/etype/cbfs.py
+++ b/tools/binman/etype/cbfs.py
@@ -296,3 +296,8 @@
         # so that child.data is used to pack into the FIP.
         self.ObtainContents(skip_entry=child)
         return True
+
+    def AddBintools(self, btools):
+        super().AddBintools(btools)
+        for entry in self._entries.values():
+            entry.AddBintools(btools)