Exynos: Clock: Cleanup soc_get_periph_rate

Since we have src, div and pre-div mask bits defined corresponding
to peripherals, calculation of clock specific to I2C appears
redundant and confusing. Using clk_bit_info struct we can write
calculations generic to all peripherals which makes code easy to
understand and free from peripheral specific exceptions.

Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>