Register cpuidle platform device on Exynos4x12 SoCs allowing EXYNOS
cpuidle driver usage on these SoCs.

AFTR mode reduces power consumption on Trats2 board (Exynos4412 SoC
with secure firmware enabled) by ~12% when EXYNOS cpuidle driver is
enabled (in both cases the default exynos_defconfig config is used
and CPU1-3 are offlined).

Currently Exynos4412 SoC support is limited to Trats2 board.
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>