Migrate arm_global_timer driver to the new 'set-state' interface
provided by the 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.
Acked-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: NMaxime Coquelin <maxime.coquelin@st.com>
Acked-by: NSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.com>
Cc: Maxime Coquelin <maxime.coquelin@st.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>