style(xilinx): replace ARM by Arm in copyrights

The commit 6bb49c876c75 ("style(hooks): adds Arm copyright style fix")
is enforcing proper case for ARM. That's why fix it in plat/xilinx to
make sure that pre-commit.copyright won't be touching platform specific
files.

Change-Id: I49c66e18d46ed871a6aa128c9b2a403d0cf83416
Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/plat/xilinx/zynqmp/tsp/tsp-zynqmp.mk b/plat/xilinx/zynqmp/tsp/tsp-zynqmp.mk
index 318b01d..f91a04c 100644
--- a/plat/xilinx/zynqmp/tsp/tsp-zynqmp.mk
+++ b/plat/xilinx/zynqmp/tsp/tsp-zynqmp.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2014, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2014, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause