arm/arm64: KVM: vgic: kill VGIC_NR_IRQS

Nuke VGIC_NR_IRQS entierly, now that the distributor instance
contains the number of IRQ allocated to this GIC.

Also add VGIC_NR_IRQS_LEGACY to preserve the current API.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --cc include/kvm/arm_vgic.h
Simple merge

diff --cc virt/kvm/arm/vgic.c
Simple merge