clockevents/drivers/asm9260: Migrate to new 'set-state' interface

Migrate asm9260 driver to the new 'set-state' interface provided by
clockevents core, the earlier 'set-mode' interface is marked obsolete
now.

As a default the timer was stopped when entering in the set_mode(RESUME)
function, now this is done explicitly with the new API.

This also enables us to implement callbacks for new states of clockevent
devices, for example: ONESHOT_STOPPED.

Cc: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>