sandbox: Enable mmc command and legacy images

The mmc command is useful for testing mmc disk images in sandbox, so
enable it. We also need to enable legacy images so that we can run tests
which use them.

Disable it for a few avb tests since MMC is not implemented there yet.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/tests/test_android/test_avb.py b/test/py/tests/test_android/test_avb.py
index a3f8831..bc5c5b5 100644
--- a/test/py/tests/test_android/test_avb.py
+++ b/test/py/tests/test_android/test_avb.py
@@ -39,6 +39,7 @@
 
 @pytest.mark.buildconfigspec('cmd_avb')
 @pytest.mark.buildconfigspec('cmd_mmc')
+@pytest.mark.notbuildconfigspec('sandbox')
 def test_avb_mmc_uuid(u_boot_console):
     """Check if 'avb get_uuid' works, compare results with
     'part list mmc 1' output
@@ -97,6 +98,7 @@
 
 @pytest.mark.buildconfigspec('cmd_avb')
 @pytest.mark.buildconfigspec('cmd_mmc')
+@pytest.mark.notbuildconfigspec('sandbox')
 def test_avb_mmc_read(u_boot_console):
     """Test mmc read operation
     """