all: Update copyright header in all files

This patch updates copyright header in all files as follows:
1. Makes "SPDX-License-Identifier: BSD-2-Clause" as first line
2. Change copyright year to 2019 for Western Digital

Signed-off-by: Anup Patel <anup.patel@wdc.com>

firmware/fw_base.ldS

@@ -1,10 +1,10 @@
 /*
- * Copyright (c) 2018 Western Digital Corporation or its affiliates.
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2019 Western Digital Corporation or its affiliates.
  *
  * Authors:
  *   Anup Patel <anup.patel@wdc.com>
- *
- * SPDX-License-Identifier: BSD-2-Clause
  */
 
 	. = FW_TEXT_START;