ARM: EXYNOS: convert cpuidle driver to be a platform driver

ARM: EXYNOS: convert cpuidle driver to be a platform driver

ARM EXYNOS cpuidle driver is currently not multiplatform support
ready (as it uses device_initcall() for initialization and doesn't
check on what platform it is running). Fix it by converting the
driver to be a platform driver and registering exynos_cpuidle
platform device from exynos[4,5]_dt_machine_init().

Signed-off-by: Bartlomiej Zolnierkiewicz <[email protected]>
Signed-off-by: Kyungmin Park <[email protected]>
Acked-by: Daniel Lezcano <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>