sandbox: Add 'sb' command to access filesystem features

The new 'sb' command is intended to deal with sandbox-specific features
that have no parallel in other archs. This commit adds two sub-commands
to list a directory and read a file from the host filesystem.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@ti.com>
diff --git a/include/config_cmd_all.h b/include/config_cmd_all.h
index 2a82e19..0930781 100644
--- a/include/config_cmd_all.h
+++ b/include/config_cmd_all.h
@@ -76,6 +76,7 @@
 #define CONFIG_CMD_RARP		/* rarpboot support		*/
 #define CONFIG_CMD_READ		/* Read data from partition	*/
 #define CONFIG_CMD_RUN		/* run command in env variable	*/
+#define CONFIG_CMD_SANDBOX	/* sb command to access sandbox features */
 #define CONFIG_CMD_SAVEENV	/* saveenv			*/
 #define CONFIG_CMD_SAVES	/* save S record dump		*/
 #define CONFIG_CMD_SCSI		/* SCSI Support			*/