clk: samsung: Add Exynos5 sub-CMU clock driver

Exynos5250/5420/5800 have only one clock controller, but some of their
clock depends on respective power domains. Handling integration of clock
controller and power domain can be done using runtime PM feature of CCF
framework. This however needs a separate struct device for each power
domain. This patch adds such separate driver for a group of such clocks,
which can be instantiated more than once, each time for a different
power domain.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>