sf: add GPL-2 license info

Some of the new spi flash files were missing explicit license lines.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

common/cmd_sf.c

@@ -2,7 +2,9 @@
  * Command for accessing SPI flash.
  *
  * Copyright (C) 2008 Atmel Corporation
+ * Licensed under the GPL-2 or later.
  */
+
 #include <common.h>
 #include <spi_flash.h>
 

drivers/mtd/spi/atmel.c

@@ -2,6 +2,7 @@
  * Atmel SPI DataFlash support
  *
  * Copyright (C) 2008 Atmel Corporation
+ * Licensed under the GPL-2 or later.
  */
 
 #include <common.h>

drivers/mtd/spi/spi_flash.c

@@ -2,6 +2,7 @@
  * SPI flash interface
  *
  * Copyright (C) 2008 Atmel Corporation
+ * Licensed under the GPL-2 or later.
  */
 
 #include <common.h>