dt-bindings: interrupt-controller: add DT binding for Marvell 7K/8K PIC

This commit adds the Device Tree binding description for the PIC
interrupt controller available in the ARM64 Marvell Armada 7K/8K SoCs.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lkml.kernel.org/r/1470408921-447-2-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>