ARM: S5P6440: Move CPU specific code in plat-s5p to machine directory

The s5p6440-clock.c and s5p6440-init.c code in the plat-s5p is specific to
s5p6440 SoC based systems. So these files are being moved to the machine
directory of s5p6440. And these files are renamed in the machine directory.

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