ARM: S5P: Reduce duplicated EPLL control codes

S5P Samsung SoCs has a EPLL to support various PLL clock sources for other
H/W blocks. Until now, to control EPLL, each of SoCs make their own functions
in 'mach-s5pxxx/clock.c'. But some of functions, 'xxx_epll_get_rate()' and
'xxx_epll_enable()', are exactly same in all S5P SoCs, so this patch move
these duplicated codes to common EPLL functions that use platform wide.

Signed-off-by: Seungwhan Youn <sw.youn@samsung.com>
Acked-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>