Add 'true' and 'false' commands

These commands are only enabled when the hush shell is enabled and can
be useful in scripts such as:

while true do
    echo "Booting OS...";
    run $bootcmd;
    echo "Booting OS failed";
    sleep 10;
done

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

common/cmd_test.c

@@ -149,3 +149,25 @@ U_BOOT_CMD(
 	"minimal test like /bin/sh",
 	"[args..]"
 );
+
+int do_false(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+{
+	return 1;
+}
+
+U_BOOT_CMD(
+	false,	CONFIG_SYS_MAXARGS,	1,	do_false,
+	"do nothing, unsuccessfully",
+	NULL
+);
+
+int do_true(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+{
+	return 0;
+}
+
+U_BOOT_CMD(
+	true,	CONFIG_SYS_MAXARGS,	1,	do_true,
+	"do nothing, successfully",
+	NULL
+);