ARM: SAMSUNG: Add plat-samsung as starting point for plat-s3c* moves

We inted to re-organise the plat-s3c/plat-s3c24xx/plat-s3c64xx into a
more generic plat-samsung with less code in the other plat- directories
to make it easier to port new devices and try and clear up some of the
naming issues with newer devices.

Start by creating a small arch/arm/plat-samsung with no actuall code in
so we can move items in as we process them.

Add this to arch/arm to allow it to build things once support is added.

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