clk: samsung: exynos3250: Add driver for CMU_ISP clock domain

Add clock controller for CMU ISP clock domain on Exynos3250,
providing clocks for FIMC-IS subsystem.

[b.michalska: use samsung_cmu_register_one to register
 the provider; updated DT binding documentation]

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Beata Michalska <b.michalska@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
[s.nawrocki: added __init attribute which was missing in function
 exynos3250_cmu_platform_init() in function, which has been]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>