ARM/davinci/time: Migrate to new 'set-state' interface

Migrate davinci 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) and so .tick_resume()
isn't implemented.

Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>