PCI: Remove unused declarations

Remove these unused declarations:

  pcibios_config_init()              # never defined anywhere
  pcibios_scan_root()                # only defined by x86
  pcibios_get_irq_routing_table()    # only defined by x86
  pcibios_set_irq_routing()          # only defined by x86

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>