S5P: Use accessor functions instead of SoC specific defines to access the base address

This patch is intended to prepare the other S5P SoC. (s5pc210)
If use SoC specific defines then can't share with other SoC.
So, make the accessor functions for access the base address by common way.

Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>