PCI: Hold pci_slot_mutex while searching bus->slots list

Previously, pci_setup_device() and similar functions searched the
pci_bus->slots list without any locking.  It was possible for another
thread to update the list while we searched it.

Add pci_dev_assign_slot() to search the list while holding pci_slot_mutex.

[bhelgaas: changelog, fold in CONFIG_SYSFS fix]
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --cc arch/powerpc/kernel/pci_of_scan.c
Simple merge

diff --cc arch/sparc/kernel/pci.c
Simple merge

diff --cc drivers/pci/probe.c
Simple merge

diff --cc drivers/pci/slot.c
Simple merge

diff --cc include/linux/pci.h
Simple merge