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

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

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: Daniel Lezcano <[email protected]>
Acked-by: Maxime Coquelin <[email protected]>
Acked-by: Srinivas Kandagatla <[email protected]>
Cc: Srinivas Kandagatla <[email protected]>
Cc: Maxime Coquelin <[email protected]>
Cc: Patrice Chotard <[email protected]>
Signed-off-by: Viresh Kumar <[email protected]>
Signed-off-by: Daniel Lezcano <[email protected]>