chore: update to use Arm word across TF-A

Align entire TF-A to use Arm in copyright header.

Change-Id: Ief9992169efdab61d0da6bd8c5180de7a4bc2244
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/include/lib/libc/stdarg.h b/include/lib/libc/stdarg.h
index e260b9b..2d1f785 100644
--- a/include/lib/libc/stdarg.h
+++ b/include/lib/libc/stdarg.h
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 /*
- * Portions copyright (c) 2018, ARM Limited and Contributors.
+ * Portions copyright (c) 2018, Arm Limited and Contributors.
  * All rights reserved.
  */