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/bsection.py b/tools/binman/bsection.py
index 07c72d3..331f806 100644
--- a/tools/binman/bsection.py
+++ b/tools/binman/bsection.py
@@ -201,6 +201,7 @@
         pos = 0
         prev_name = 'None'
         for entry in self._entries.values():
+            entry.CheckPosition()
             if (entry.pos < self._skip_at_start or
                 entry.pos >= self._skip_at_start + self._size):
                 entry.Raise("Position %#x (%d) is outside the section starting "