PCI: Separate pci_bus_read_dev_vendor_id from pci_scan_device

PCI: Separate pci_bus_read_dev_vendor_id from pci_scan_device

Orabug:13993738
We can reuse it for pciehp probing.

-v2: according to Kenji, fix crs timeout checking, and export the function
     for later use when pciehp is compiled as a module.

Suggested-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
(cherry picked from commit efdc87dab1cdf25ba631181ac0ead3fb2023dd10)

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>