ARM: ux500: convert timer suspend/resume to clock_event_device

Move ux500's timer suspend/resume functions from struct sys_timer
ux500_timer into struct clock_event_device nmdk_clkevt. This
will allow the sys_timer suspend/resume fields to be removed, and
eventually lead to a complete removal of struct sys_timer.

Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>