ARMV7: S5P: separate the peripheral clocks

Because of peripheral devices can select clock sources,
separate the peripheral clocks. (pwm, uart and so on)
It just return the pclk at s5pc1xx SoC,
but s5pc210 SoC must be calculated by own clock register setting.

Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>