virtio_pci: move probe to common file

It turns out this make everything easier.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --cc drivers/virtio/virtio_pci_common.c
Simple merge

diff --cc drivers/virtio/virtio_pci_common.h
Simple merge

diff --cc drivers/virtio/virtio_pci_legacy.c
Simple merge