binman: Correct some import statements

Some of these were not converted when binman moved to use absolute paths.
Fix them.

Also drop the import of 'test' which is a directory, not a module.

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

tools/binman/ftest.py

@@ -29,7 +29,7 @@ from dtoc import fdt
 from dtoc import fdt_util
 from binman.etype import fdtmap
 from binman.etype import image_header
-from image import Image
+from binman.image import Image
 from patman import command
 from patman import test_util
 from patman import tools