Allows edk2 detect virtio-mmio devices and pcie ecam.
See comment in hw/i386/microvm-dt.c for more details.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Message-Id: <20211014193617.2475578-1-kraxel@redhat.com>