cpuidle: Add common time keeping and irq enabling

cpuidle: Add common time keeping and irq enabling

Make necessary changes to implement time keeping and irq enabling
in the core cpuidle code.  This will allow the removal of these
functionalities from various platform cpuidle implementations whose
timekeeping and irq enabling follows the form in this common code.

Signed-off-by: Robert Lee <[email protected]>
Tested-by: Jean Pihet <[email protected]>
Tested-by: Amit Daniel <[email protected]>
Tested-by: Robert Lee <[email protected]>
Reviewed-by: Kevin Hilman <[email protected]>
Reviewed-by: Daniel Lezcano <[email protected]>
Reviewed-by: Deepthi Dharwar <[email protected]>
Acked-by: Jean Pihet <[email protected]>
Signed-off-by: Len Brown <[email protected]>