clockevents: Add helpers to check the state of a clockevent device

clockevents: Add helpers to check the state of a clockevent device

Some clockevent drivers, once migrated to use per-state callbacks,
need to check the state of the clockevent device in their callbacks or
interrupt handler.

Add accessor functions clockevent_state_*() to get this information.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linaro-kernel@lists.linaro.org
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/04a717d490335c688dd7af899fbcede97e1bb8ee.1432192527.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit 3434d23b694e5cb6e44e966914563406c31c4053)

As hv drivers depends on it
Orabug: 21886720
Signed-off-by: Jason Luo <zhangqing.luo@oracle.com>