clksrc: delete nomadik MTU non-DT boot path

Both platforms using the MTU (Nomadik and Ux500) have now been
converted to use device tree exclusively, thus let us delete
this platform data header and make this driver a fully
self-contained DT-only driver.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Lee Jones <lee.jones@linaro.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>