pci romfiles: add property, add default to PCIDeviceInfo
This patch adds a romfile property to the pci bus. It allows to specify
a romfile to load into the rom bar of the pci device. The default value
comes from a new field in PCIDeviceInfo. The property allows to change
the file and also to disable the rom loading using an empty string.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>