Commit 1c380f94

 breaks live migration.
DMA stops working for ehci (and probably for any pci device) after
restoring the guest because the bus master region never gets enabled.
Add code doing that after loading the pci config space from vmstate.

Cc: Avi Kivity <avi@redhat.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>