This patch reworks the clock binding to avoid too much detail in DT.
Now we have only compatible string per type of clock
(remark from Rob https://lkml.org/lkml/2016/5/25/492

)

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>