ARM: ux500: convert to twd_local_timer_register() interface

Add support for the new smp_twd runtime registration interface
to the ux500 platforms, and remove the old compile-time support.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>