x86: apl: Add the term "Interrupt Timer Subsystem" to ITSS files

ITSS stands for "Interrupt Timer Subsystem", so add that term to the
description of the relevant files.

Signed-off-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/include/asm/arch-apollolake/itss.h b/arch/x86/include/asm/arch-apollolake/itss.h
index 1e29503..c75d8fe 100644
--- a/arch/x86/include/asm/arch-apollolake/itss.h
+++ b/arch/x86/include/asm/arch-apollolake/itss.h
@@ -1,5 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
+ * Interrupt Timer Subsystem
+ *
  * Copyright (C) 2017 Intel Corporation.
  * Copyright 2019 Google LLC
  *