clk: versatile: Export icst_clk_setup()

Export this clock setup method so we can register the
IM-PD1 clocks with common code in the next step.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lkml.kernel.org/r/20200219103326.81120-2-linus.walleij@linaro.org


Signed-off-by: Stephen Boyd <sboyd@kernel.org>