This adds support for the ARM syscon ICST clocks to initialized
directly from the device tree syscon node on ARM Integrator,
Versatile and RealView reference designs.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-clk@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>