spi: Add GPL-2.0+ SPDX-License-Identifier for missing files

Added GPL-2.0+ SPDX-License-Identifier for missed spi
source files.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
diff --git a/drivers/spi/altera_spi.c b/drivers/spi/altera_spi.c
index b53607a..5accbb5 100644
--- a/drivers/spi/altera_spi.c
+++ b/drivers/spi/altera_spi.c
@@ -5,7 +5,7 @@
  * Copyright (c) 2005-2008 Analog Devices Inc.
  * Copyright (C) 2010 Thomas Chou <thomas@wytron.com.tw>
  *
- * Licensed under the GPL-2 or later.
+ * SPDX-License-Identifier:	GPL-2.0+
  */
 #include <common.h>
 #include <asm/io.h>