ARM: pxa: convert timer suspend/resume to clock_event_device

Move PXA's timer suspend/resume functions from struct sys_timer
pxa_timer into struct clock_event_device ckevt_pxa_osmr0. This
will allow the sys_timer suspend/resume fields to be removed, and
eventually lead to a complete removal of struct sys_timer.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>