clk: exynos: add clock driver for Exynos7420 Soc

Add a clock driver for Exynos7420 SoC. There are about 25 clock controller
blocks in Exynos7420 out of which support for topc, top0 and peric1 blocks
are added in this initial version of the driver.

Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>