pci: untangle pci/msi dependency

pci: untangle pci/msi dependency

msi depends on pci but pci should not depend on msi.
The only dependency we have is a recent addition
of pci_msi_ functions, IMO they add little enough to
open-code in the small number of users.

Follow-up patches add more cleanups.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>