clk: samsung: dt-bindings: Document Exynos5433 IMEM CMU

Document DT bindings of the IMEM CMU providing clocks for the Exynos5433
Security SubSystem (SSS) and SlimSSS IPs.

Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Kamil Konieczny <k.konieczny@partner.samsung.com>
[s.nawrocki@samsung.com: edited commit description]
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>