arm: total_compute: Support Debian boot

Add booting option for Debian system.

Signed-off-by: Leo Yan <leo.yan@arm.com>
diff --git a/board/armltd/total_compute/total_compute.env b/board/armltd/total_compute/total_compute.env
index 93460aa..7924632 100644
--- a/board/armltd/total_compute/total_compute.env
+++ b/board/armltd/total_compute/total_compute.env
@@ -31,5 +31,9 @@
     elif iminfo ${load_addr}; then
         echo 'Booting FIT image...';
         bootm ${load_addr} ${load_addr} ${fdt_addr_r};
+    else;
+        echo 'Booting Debian...';
+        set bootargs $bootargs root=/dev/mmcblk0p1 rw;
+        booti ${kernel_addr_r} - ${fdt_addr_r};
     fi;
     echo 'ERROR: No valid image to boot the system. Aborting boot sequence.';