arm64: dts: renesas: r8a774b1: Add INTC-EX device node

Add support for the Interrupt Controller for External Devices
(INTC-EX) on RZ/G2N.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Link: https://lore.kernel.org/r/1570531132-21856-11-git-send-email-fabrizio.castro@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>