tests/libqos: Add loongarch virt machine node

tests/libqos: Add loongarch virt machine node

Add loongarch virt machine to the graph. It is a modified copy of
the existing riscv virtmachine in riscv-virt-machine.c

It contains a generic-pcihost controller, and an extra function
loongarch_config_qpci_bus() to configure GPEX pci host controller
information, such as ecam and pio_base addresses.

Also hotplug handle checking about TYPE_VIRTIO_IOMMU_PCI device is
added on loongarch virt machine, since virtio_mmu_pci device requires
it.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20240528082053.938564-1-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>