ARM: OMAP4: cpuidle: use init/exit common routine

Remove the duplicated code and use the cpuidle common code for initialization.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>