ARM: S5P64X0: Update Clock for S5P6440 and S5P6450

This patch updates regarding clock files for supporting S5P6440 and
S5P6450 with one kernel image. The mach-s5p64x0/clock.c is for common
of them and there are specific clock files for each SoCs.

Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>