xen/arm: Deliver interrupts to vcpu specified in IROUTER

xen/arm: Deliver interrupts to vcpu specified in IROUTER

In GICv3 use IROUTER register contents to deliver irq to
specified vcpu.

vgic irouter[irq] is used to represent vcpu number for which
irq affinity is assigned. Bit[31] is used to store IROUTER
bit[31] value to represent irq mode.

This patch is similar to Stefano's commit
5b3a817ea33b891caf7d7d788da9ce6deffa82a1 for GICv2

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>