clk: versatile add DT bindings for the ICST CM variants

The Integrator/AP and Integrator/CP core modules have special
versions of the ICST525 interface hardcoding some bits. Create
special compatible strings to identify these variants, also
explain a bit what is going on.

Cc: devicetree@vger.kernel.org
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>