clk: samsung: add initial clock support for Exynos7 SoC

Add initial clock support for Exynos7 SoC which is required
to bring up platforms based on Exynos7.

Signed-off-by: Naveen Krishna Ch <naveenkrishna.ch@gmail.com>
Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Reviewed-by: Thomas Abraham <thomas.ab@samsung.com>
Tested-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>