virtio_pci: move probe/remove code to common

Most of initialization is device-independent.
Let's move it to common.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

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