[ARM] S3C24XX: Fix SERIAL_SAMSUNG entry

The SERIAL_SAMSUNG needs SERIAL_CORE but doesn't select it, leading to a
build failure. Adding a 'select SERIAL_CORE' cure the trouble.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>