rtc: s3c: Integrate Exynos3250 into S3C6410

There are now no differences between RTC on Exynos3250 and S3C6410.
Merge everything into one so duplicated code could be removed.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>