ARM: shmobile: convert to twd_local_timer_register() interface

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

Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>