hw/arm/virt: Add linux,pci-domain property

hw/arm/virt: Add linux,pci-domain property

This allows to pin the host controller in the Linux PCI domain space.
Linux requires that property to be available consistently or not at all,
in which case the domain number becomes unstable on additions/removals.
Adding it here won't make a difference in practice for most setups as we
only expose one controller.

However, enabling Jailhouse on top may introduce another controller, and
that one would like to have stable address as well. So the property is
needed for the first controller as well.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Message-id: 3301c5bc-7b47-1b0e-8ce4-30435057a276@web.de
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>