test: dm: virtio: Add test cases for virtio uclass

Now that we have a sandbox virtio transport driver, add some test
cases to test virtio uclass driver.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_noblk_defconfig b/configs/sandbox_noblk_defconfig
index 93b2240..e71e2d3 100644
--- a/configs/sandbox_noblk_defconfig
+++ b/configs/sandbox_noblk_defconfig
@@ -171,6 +171,7 @@
 CONFIG_VIDEO_SANDBOX_SDL=y
 CONFIG_OSD=y
 CONFIG_SANDBOX_OSD=y
+# CONFIG_VIRTIO_BLK is not set
 CONFIG_FS_CBFS=y
 CONFIG_FS_CRAMFS=y
 CONFIG_CMD_DHRYSTONE=y