vexpress64: fix a typo of SPDX-License-Identifier

Misspelling of SPDX-License-Identifier is rather fatal than other
general typos, so must be fixed.

This file spells SPDX-Licence-Identifier.
                           ^

I also moved it to the very top of the file with // comment style.

Detected by grepping the source tree:

$ git grep --not -e SPDX-License-Identifier --and -e SPDX-
board/armltd/vexpress64/pcie.c: * SPDX-Licence-Identifier:      GPL-2.0+

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Liviu Dudau <liviu.dudau@foss.arm.com>

board/armltd/vexpress64/pcie.c

@@ -1,9 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) ARM Ltd 2015
  *
  * Author: Liviu Dudau <Liviu.Dudau@arm.com>
- *
- * SPDX-Licence-Identifier:	GPL-2.0+
  */
 
 #include <common.h>