ARM: EXYNOS: Add flush_cache_all in suspend finisher

The core cpu_suspend code no longer calls flush_cache_all to
optimize the cpu idle flow. Add a call for the same in the
exynos specific suspend code.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>