PCI: add pci_get_domain_bus_and_slot function

Added the pci_get_domain_and_slot_function which is analogous to
pci_get_bus_and_slot. It returns a pci_dev given a domain (segment) number,
bus number, and devnr. Like pci_get_bus_and_slot,
pci_get_domain_bus_and_slot holds a reference to the returned pci_dev.

Converted pci_get_bus_and_slot to a wrapper that calls
pci_get_domain_bus_and_slot with the domain hard-coded to 0.

This routine was patterned off code suggested by Bjorn Helgaas.

Acked-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Patterson <andrew.patterson@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>