ARM: dts: imx7d: fix GIC nodes interrupt and register specification

The i.MX 7 as a GICv2, hence its CPU interface register map (the
second register region) is 8kB long. Add the VGIC maintenance
interrupt which allows to use the new VGIC driver.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Suggested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>