So we have a boot display when using a vgpu as primary display.
ramfb depends on a fw_cfg file. fw_cfg files can not be added and
removed at runtime, therefore a ramfb-enabled vfio device can't be
hotplugged.
Add a nohotplug variant of the vfio-pci device (as child class). Add
the ramfb property to the nohotplug variant only. So to enable the vgpu
display with boot support use this: