hw/intc/arm_gic(v3)_kvm: Initialize gsi routing

Advertise gsi routing and set up irqchip routing entries for
GIC SPIs.

This is not mandated as long as MSI routing is not used
(because the kernel sets a default irqchip routing table).
However once MSI routing gets used (for VIRTIO-PCI vhost for
example), the first call to KVM_SET_GSI_ROUTING overrides the
kernel default irqchip table.

If no routing entry exists for the GSI, any IRQFD signaling for
this GSI will fail.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1474616617-366-2-git-send-email-eric.auger@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
