Thermal: exynos: Add support for temperature falling interrupt.

This patch introduces using temperature falling interrupt in exynos
thermal driver. Former patch, it only use polling way to check
whether if system themperature is fallen. However, exynos SOC also
provides temperature falling interrupt way to do same things by hw.
This feature is not supported in exynos4210.

Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>