ARM: keystone: clock: move K2HK SoC dependent code in separate file

ARM: keystone: clock: move K2HK SoC dependent code in separate file

This patch in general spit SoC type clock dependent code and general
clock code. Before adding keystone II Edison k2e SoC which has
slightly different dpll set, move k2hk dependent clock code to
separate clock-k2hk.c file.

Acked-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>