clk/realview: stop using machine headers

In order to move realview into multiplatform, we have to prevent device
drivers from accessing the machine header files.

In case of the clk driver, this is very simple, we just copy the
small set of register definitions into the driver that needs them.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>