clk: samsung: Factor out the common code to clk.c

While adding clock support for Exynos5260, the infrastructure to
register multiple clock controllers was introduced. Factor out the
support for registering multiple clock controller from Exynos5260
clock code to common samsung clock code so that it can be used by
other Exynos SoC which have multiple clock controllers.

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>