PCI: drivers/pci/pci.c: add prototypes

This patch adds prototypes for pcibios_disable_device() and
pcibios_set_pcie_reset_state() in include/linux/pci.h

While I was at it, I also removed the unneeded "extern" from the
prototype of pcibios_add_platform_entries().

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>