arm64: dts: Add maintenance interrupt for GIC in NS2 DT

The KVM ARM64 requires GIC maintenance interrupt for VGIC emulation
so this patch adds the missing "interrupts" attribute to GIC node in
NS2 DT.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>