ARM: dts: ux500: Add clkout-clock node

This adds the DTS node and picks up the include file from the
bindings required to obtain externally routed CLKOUT1 and CLKOUT2
clocks.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>