xen/arm: IRQ: Do not allow IRQ to be shared between domains and XEN

xen/arm: IRQ: Do not allow IRQ to be shared between domains and XEN

The current dt_route_irq_to_guest implementation sets IRQ_GUEST even if the
IRQ is correctly setup.

An IRQ can be shared between devices, if the devices are not assigned to the
same domain or Xen, then this could result in routing the IRQ to the domain
instead of Xen ...

Also avoid to relying on wrong the behaviour when Xen is routing an IRQ to
DOM0. Therefore check the return code from route_dt_irq_to_guest in
map_device.

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