binman: Add support for sections

It is useful to be able to split an image into multiple sections,
each with its own size and position, for cases where a flash device has
read-only and read-write portions.

Add support for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index 5374178..8b46fbb 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -220,3 +220,12 @@
           section: Section containing the entry
         """
         pass
+
+    def CheckPosition(self):
+        """Check that the entry positions are correct
+
+        This is used for entries which have extra position requirements (other
+        than having to be fully inside their section). Sub-classes can implement
+        this function and raise if there is a problem.
+        """
+        pass