group/tf-l3-boot-tests-css: Add boot test config for Morello

Add support to fetch the SCP and MCP binaries
from the prebuilts and add boot test config for
Morello FVP platform in group/tf-l3-boot-tests-css.

Also, the grub-busybox.img file has been renamed as busybox.img
in the latest software stack for Morello Platform.

Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
Change-Id: I8d1533c72c64f9eb5e82c95123a5edda7fa733f7
diff --git a/group/tf-l3-boot-tests-css/fvp-morello-default:fvp-linux.morello-fip.morello-morello-debug b/group/tf-l3-boot-tests-css/fvp-morello-default:fvp-linux.morello-fip.morello-morello-debug
new file mode 100644
index 0000000..aa57540
--- /dev/null
+++ b/group/tf-l3-boot-tests-css/fvp-morello-default:fvp-linux.morello-fip.morello-morello-debug
@@ -0,0 +1,5 @@
+#
+# Copyright (c) 2021, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#