PCI: Remove unused "pci_probe" flags

The following flags are only used on x86, but they got copied to FR-V,
MN10300, and SuperH:

  PCI_PROBE_BIOS
  PCI_PROBE_CONF1
  PCI_PROBE_CONF2
  PCI_ASSIGN_ROMS
  PCI_NO_CHECKS
  PCI_BIOS_IRQ_SCAN
  PCI_ASSIGN_ALL_BUSSES

FR-V and MN10300 do test for PCI_ASSIGN_ROMS, but they never set it, so
it's dead code.

Remove the unused flags above.

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