When transitioning some elder platforms to device tree it
becomes necessary to cascade VIC IRQ chips off another
interrupt controller.

Tested with the cascaded VIC on the Integrator/AP attached
logic module IM-PD1.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200219153543.137153-1-linus.walleij@linaro.org