ARM: SAMSUNG: Use PLAT_SAMSUNG instead of PLAT_S3C

As part of the development process, it is hoped PLAT_S3C is either removed
from all of the PLAT_SAMSUNG derived platforms or removed entirely. It is
also better to use PLAT_SAMSUNG as this is the current base of all Samsung
devices.

Change the two places that use PLAT_S3C to use PLAT_SAMSUNG

Signed-off-by: Ben Dooks <ben-linux@fluff.org>