clk: samsung: exynos-clkout: Convert to the new clk_hw API

Clock providers should use the new struct clk_hw based API, so convert
Exynos CLKOUT clock provider to the new approach.

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>