PCI: Reorder so actual code comes before stubs

Consistently use the:

    #ifdef CONFIG_PCI_FOO
    int pci_foo(...);
    #else
    static inline int pci_foo(...) { return -1; }
    #endif

pattern, instead of sometimes using "#ifndef CONFIG_PCI_FOO".

No functional change.

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