virtio_pci: update file descriptions and copyright

There's been a lot of changes since 2007.
List main authors, add Red Hat copyright.

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

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

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

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