ARM: integrator: get the LM interrupts from DT

The OF/DT boot path needs to get the LM (Logical Module)
IRQs from the device tree for coherency. This augments the
DT syscon node to contain these IRQs and alter the DT LM
code to get them from there.

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