m68k/coldfire/pit: Migrate to new 'set-state' interface

Migrate m68k 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: Greg Ungerer <gerg@uclinux.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>