xen/arm: Allow virq != irq

xen/arm: Allow virq != irq

Currently, Xen is assuming that the virtual IRQ will always be the same
as IRQ.

Modify route_guest_irq to take the virtual IRQ in parameter which allow
Xen to assign a different IRQ number. Also store the vIRQ in the desc
action to easily retrieve the IRQ target when we need to inject the
interrupt.

As DOM0 will get most the devices, the vIRQ is equal to the IRQ in that case.

At the same time modify the behavior of irq_get_domain. The function now
requires that the irq_desc belongs to an IRQ assigned to a guest.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>