ARM: sa1100: convert timer suspend/resume to clock_event_device

Move sa1100's timer suspend/resume functions from struct sys_timer
sa1100_timer into struct clock_event_device ckevt_sa1100_osmr0. This
will allow the sys_timer suspend/resume fields to be removed, and
eventually lead to a complete removal of struct sys_timer.

Signed-off-by: Stephen Warren <swarren@nvidia.com>