arm/vgic: vgic: support irq enable/disable

arm/vgic: vgic: support irq enable/disable

If vgic_vcpu_inject_irq is called (for example by a device emulator like
vtimer.c) but the corresponding irq is not enabled in the virtual gicd
just queue it in the inflight_irqs list.

When the irq is enabled make sure to call gic_set_guest_irq.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>