ARM: S5P: Cleanup the S5P SoCs' VA address mapping

Basically S5P SoCs use the Samsung common VA address mapping where
plat-samsung and use plat-s5p's mapping also. The later is a little
mess. So this patch cleans it up.

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>