ARM: ux500: Move timer code to separate file

Just split off the timer code to its own file so we have a
more fine-grained file tree.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>