binman: Update entry.SetOffsetSize to be optional

At present this function always sets both the offset and the size of
entries. But in some cases we want to set only one or the other, for
example with the forthcoming ifwi entry, where we only set the offset.
Update the function to handle this.

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

tools/binman/entry.py

@@ -368,13 +368,21 @@ class Entry(object):
             Dict:
                 key: Entry type
                 value: List containing position and size of the given entry
-                    type.
+                    type. Either can be None if not known
         """
         return {}
 
-    def SetOffsetSize(self, pos, size):
-        self.offset = pos
-        self.size = size
+    def SetOffsetSize(self, offset, size):
+        """Set the offset and/or size of an entry
+
+        Args:
+            offset: New offset, or None to leave alone
+            size: New size, or None to leave alone
+        """
+        if offset is not None:
+            self.offset = offset
+        if size is not None:
+            self.size = size
 
     def SetImagePos(self, image_pos):
         """Set the position in the image