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

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

We weren't doing anything in set_mode(RESUME) except of
local_irq_{save|restore}(), which isn't required and so ->tick_resume
isn't implemented.

Cc: Eric Miao <eric.y.miao@gmail.com>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>