clk: Tag basic clk types with SPDX

These are all GPL-2.0 files per the existing license text. Replace the
boiler plate with the tag.

Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk-gate.c

@@ -1,11 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2010-2011 Canonical Ltd <jeremy.kerr@canonical.com>
  * Copyright (C) 2011-2012 Mike Turquette, Linaro Ltd <mturquette@linaro.org>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  * Gated clock implementation
  */