clk: add GPLv2 headers to the Versatile clock files

The GPLv2 headers were missing and the subsystem maintainer likes
them so put them in. I am the copyright holder, so explicitly
licensing these under the GPLv2.

Reported-by: Mike Turquette <mturquette@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>