arm: debug: replace license blocks with SPDX

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/include/linux/serial_reg.h b/include/linux/serial_reg.h
index 99b4705..9214b67 100644
--- a/include/linux/serial_reg.h
+++ b/include/linux/serial_reg.h
@@ -2,9 +2,8 @@
  * include/linux/serial_reg.h
  *
  * Copyright (C) 1992, 1994 by Theodore Ts'o.
- * 
- * Redistribution of this file is permitted under the terms of the GNU 
- * Public License (GPL)
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
  * 
  * These are the UART port assignments, expressed as offsets from the base
  * register.  These assignments should hold for any serial port based on