ARM: integrator: get the CM control register by proxy

ARM: integrator: get the CM control register by proxy

The CM_CTRL register was accessed directly from the LED driver,
which does not work now that we get the base for the register
from the device tree. Add an accessor function to do this and
make the LED driver compile again.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>