ARM: EXYNOS: Encapsulate the AFTR code into a function

Let's encapsulate the AFTR state specific call into a single function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>