Add a simple test which checks that a sandbox-emulated SD card can be used
correctly. This tests plumbing through the MMC stack's block-device
implementaion.
Signed-off-by: Simon Glass <sjg@chromium.org>
Add a test to confirm that we can probe this device. Since there is no
MMC stack support in sandbox at present, this is as far as the test goes.
Signed-off-by: Simon Glass <sjg@chromium.org>