PCI: Move pci_set_flags() from asm-generic/pci-bridge.h to linux/pci.h

The PCI flag management constants and functions were previously declared in
include/asm-generic/pci-bridge.h.  But they are not specific to bridges,
and arches did not include pci-bridge.h consistently.

Move the following interfaces and related constants to include/linux/pci.h
and remove pci-bridge.h:

  pci_set_flags()
  pci_add_flags()
  pci_clear_flags()
  pci_has_flag()

This fixes these warnings when building for some arches:

  drivers/pci/host/pcie-designware.c:562:20: error: 'PCI_PROBE_ONLY' undeclared (first use in this function)
  drivers/pci/host/pcie-designware.c:562:7: error: implicit declaration of function 'pci_has_flag' [-Werror=implicit-function-declaration]

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>