binman: Change how faked blobs are created

At present fake blobs are created but internally an empty blob is used.
Change it to use the contents of the faked file. Also return whether the
blob was faked, in case the caller needs to know that.

Add a TODO to put fake blobs in their own directory.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
diff --git a/tools/binman/binman.rst b/tools/binman/binman.rst
index 509fc8d..935839c 100644
--- a/tools/binman/binman.rst
+++ b/tools/binman/binman.rst
@@ -1500,7 +1500,8 @@
 - Figure out how to make Fdt support changing the node order, so that
   Node.AddSubnode() can support adding a node before another, existing node.
   Perhaps it should completely regenerate the flat tree?
-
+- Put faked files into a separate subdir and remove them on start-up, to avoid
+  seeing them as 'real' files on a subsequent run
 
 --
 Simon Glass <sjg@chromium.org>