Some of these tests don't actually check anything. Add a few more checks
to complete the tests.
Also add a simple scan test that does the basics.
Signed-off-by: Simon Glass <sjg@chromium.org>
Move the tests related to scanning into their own class, updating them
to avoid using dtb_platdata as a pass-through.
Signed-off-by: Simon Glass <sjg@chromium.org>