sandbox: enable CONFIG_CMD_FS_GENERIC

Since the generic ls command no longer segfaults sandbox, enable it.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/sandbox.h b/include/configs/sandbox.h
index a6d5582..e77d06b 100644
--- a/include/configs/sandbox.h
+++ b/include/configs/sandbox.h
@@ -42,6 +42,7 @@
 #define CONFIG_CMD_PART
 #define CONFIG_DOS_PARTITION
 #define CONFIG_HOST_MAX_DEVICES 4
+#define CONFIG_CMD_FS_GENERIC
 
 #define CONFIG_SYS_VSNPRINTF