PCI: reserve bus range for SR-IOV device

Reserve the bus number range used by the Virtual Function when
pcibios_assign_all_busses() returns true.

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>