The versatile dts is missing any clock data. Add the clocks.

It is not clear from the documentation where pclk comes from, so for
now it is a dummy clock which is sufficient for things to work.
Signed-off-by: NRob Herring <robh@kernel.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>